ZXR250 - hesitation and stalls when warm

[Grasshopperus]

Hi there,
I've got a 1990 Kawasaki ZXR250, 4-cylinder, 4-stroke and it's got a problem.

The bike starts quickly and happily when it's cold. I put the choke on for a little while and after a minute i turn it off. I then jump on the bike and head out for a ride. After a while (at least 20 minutes) the bike will sometimes stall when I stop giving it gas ie. come to an intersection or set of lights. When it stalls the revs slowly decrease from around 1500rpm to zero, I can see it happening and have become adept at keeping up the revs as I slow down.

After it stalls it becomes very difficult to start again. The battery is new and it tries pretty hard to start again but i usually have to wait up to a minute for it to catch.

I also have a problem with throttle hesitation. When I open the throttle up quickly (not just close then full open, also from say 30% throttle) it bogs down until it gets to around 10K revs and then pulls alright until red-line of 19K. I don't usually give it that many revs so that is just FYI.

I've seen there are people posting similar threads at the moment but this situation is a little different. I'm not sure if the differences are important or not. I'm not a mechanic so pretty unsure.

The weird thing is that it starts fine when cold and idles happily. When I get home after a decent ride (where I've had it stall) it'll happily sit in my garage idling as if nothing happened.

Can anyone help?

[gwigs]

Could be many things,check out this site..http://www.dansmc.com/mc_repaircourse.htm
number 10 .trouble shooting

[Grasshopperus]

Could be many things,check out this site..http://www.dansmc.com/mc_repaircourse.htm
number 10 .trouble shooting

Thanks mate, that site is awesome!

[wrenchjockey]

hi,you dont say if the bogging down is worse when hot.my guess is it will be.how many miles has it done?i would think that there is wear on the needles and needle jets making the bike run rich in the mid range.you may be able to lower the slide needles if!! they are adjustable.also make sure the float heights are correct.not to high.before you start changing carb settings i would check valve clearances.could also cause this problem(if they are tight)i have been repairing bikes for over 35 years and the high preformance 250 4"s can be very tricky to get right as they get older. regards barry

[Harris Ang]

Just had the same problem today.. But I didn't let the bike warm up before riding.. Hopefully it'll go away after 2-3 mins of warming up.. crossfingers.. if not.. Service!:facepalm:

[tigertim20]

sounds similarto myold FZR.the diagnosis was carbon buildup around the valves, which eventually got t othe point where the valves couldnt seal properly and she wouldnt go at all

[Rhys]

Have you tried giving it a hard ride lots of full throttle with plenty of revs! They can start to run a little ruff if not ridden hard, or if its had lots of town or low speed riding.
Bit like a lot of 2 strokes :scooter:

[racefactory]

Hi there,
I've got a 1990 Kawasaki ZXR250, 4-cylinder, 4-stroke and it's got a problem.

The bike starts quickly and happily when it's cold. I put the choke on for a little while and after a minute i turn it off. I then jump on the bike and head out for a ride. After a while (at least 20 minutes) the bike will sometimes stall when I stop giving it gas ie. come to an intersection or set of lights. When it stalls the revs slowly decrease from around 1500rpm to zero, I can see it happening and have become adept at keeping up the revs as I slow down.

After it stalls it becomes very difficult to start again. The battery is new and it tries pretty hard to start again but i usually have to wait up to a minute for it to catch.

I also have a problem with throttle hesitation. When I open the throttle up quickly (not just close then full open, also from say 30% throttle) it bogs down until it gets to around 10K revs and then pulls alright until red-line of 19K. I don't usually give it that many revs so that is just FYI.

I've seen there are people posting similar threads at the moment but this situation is a little different. I'm not sure if the differences are important or not. I'm not a mechanic so pretty unsure.

The weird thing is that it starts fine when cold and idles happily. When I get home after a decent ride (where I've had it stall) it'll happily sit in my garage idling as if nothing happened.

Can anyone help?

Everything you describe fits the description of a rich condition. If it starts up straight away when cold especially without choke then it is running rich on the low speed circuit/pilot jet/idle jet.

If it pulls nicely up top then the main jetting is good. Set your pilot screws to factory settings in the manual. Your needles could be worn, letting excess fuel through to cause a rich condition that would explain your slow revving to 10k. Try putting the clips up one notch on the needles and see if it makes it better.

[ducatilover]

Everything you describe fits the description of a rich condition. If it starts up straight away when cold especially without choke then it is running rich on the low speed circuit/pilot jet/idle jet.

If it pulls nicely up top then the main jetting is good. Set your pilot screws to factory settings in the manual. Your needles could be worn, letting excess fuel through to cause a rich condition that would explain your slow revving to 10k. Try putting the clips up one notch on the needles and see if it makes it better.

Racefactory beat me to it.


Check your airfilter too, if in doubt, replace it, they're cheap and your bike will love you.
I'd gamble your needles are in need of replacing though.
But, a lot of those smaller bikes won't pull cleanly at full throttle below 10,000. Roll the throttle on and see what happens.

[Harris Ang]

So yea, bike WAS running rich probably because I was using 98 instead of 91 :facepalm: so far haven't had an engine stall..

"Rhys

Have you tried giving it a hard ride lots of full throttle with plenty of revs! They can start to run a little ruff if not ridden hard, or if its had lots of town or low speed riding.
Bit like a lot of 2 strokes "

If i were to nanny ride it all the time ie not thrash it.. 10k+ revs will it do more damage than good? Or is it good to thrash it once in a while?

[tigertim20]

So yea, bike WAS running rich probably because I was using 98 instead of 91 :facepalm: so far haven't had an engine stall..

"Rhys

Have you tried giving it a hard ride lots of full throttle with plenty of revs! They can start to run a little ruff if not ridden hard, or if its had lots of town or low speed riding.
Bit like a lot of 2 strokes "

If i were to nanny ride it all the time ie not thrash it.. 10k+ revs will it do more damage than good? Or is it good to thrash it once in a while?

theyre built with an 18k redline or so. high rpm isnt going to hurt it, jesus they do near 10k just sitting at the open road speed limit. nothing wrong with revving it man, its a sportsbike, thats what it was built for

[racefactory]

theyre built with an 18k redline or so. high rpm isnt going to hurt it, jesus they do near 10k just sitting at the open road speed limit. nothing wrong with revving it man, its a sportsbike, thats what it was built for

Yup what he says. These bikes have proven to last forever at 20k rpm on the race track.

[Ultrasonic2]

WOOOO HOOOO

some else with the same bike and the same problems . i also took it to a place and they didn't know what was wrong with it too.

I also have EXACTLY THE SAME ISSUES AS YOU. TO THE LETTER !!

Now i also went down a track for AGES thinking the bike was Rich but that was TOTALLY WRONG

The bike is WAY to lean

i presume this bike isn't stock any more and it's now way to lean

With the pilot screws at the 2.5 turns out my bike at the lights will idle lower and lower until it stops. The bike is to lean you need to increase the turns to 2 3/4 to 3 turns. this will allow your bike to idle again. you will also notice the bike is much faster.


Now when you jam open the throttle and it dies alot of people will say it's rich. in this case they are wrong. again the bike is miles to lean and you need to start increase the main jets on the bike like i have.

The cool thing is i know your bike must be slow as and once you increase the fuel the thing will fly like you couldn't imagine.

[ducatilover]

Pilot screws will not make your bike faster, they have nothing to do with it's high RPM running, they are redundant after 3000rpm.
If it is that lean, it will be very flat in power, rich will make it surge, it will also back fire off the throttle when it's to lean.
If it has problems idling and it hesitates when hot, it's too rich.
If you rev it when warm and it drops below normal idle and climbs back up again, it's too rich.
If the revs drop slowly it's too lean, or there are sticking slides/throttles.

[Ultrasonic2]

Pilot screws will not make your bike faster, they have nothing to do with it's high RPM running, they are redundant after 3000rpm.
this is a common kiwi biker comment and i can understand why it's seemingly become law here. Obviously carbs are different so it's hard to make a blanket statement about them if the carb in question wasn't a slide carb i would tend to agree with this comment in general. With slide carbs it's a bit harder. If you search on slide crabs you'll find some people suggesting that the screw we're adjusting will affect the whole range.

At the end of the day the It's relatively easy to tell, when you dis mantel the carbs you can follow the gernals and it's pretty easy that on THIS carb it's impossible for the fuel to stop flowing through these channels.

And at the end of the day if he adjusts the screw he will crease his performance across the whole range. i know i've spent ages playing with this screw



If it is that lean, it will be very flat in power, rich will make it surge, it will also back fire off the throttle when it's to lean.
Totally agree and his power is flat but he doens't know it because he hasn't got anything to compare it against.

His bike will be heating up real fast to, too 1/2 way (where the fan comes on) but there again he does't have anything to compare against so doesn't know any better



If you rev it when warm and it drops below normal idle and climbs back up again, it's too rich.
If the revs drop slowly it's too lean, or there are sticking slides/throttles.

At the time i had my idle at 2.100 rpm and it slowing gets slower and slower and stops. increasing the fuel via the pilot screw fixes this

I have spent a year on this issue with my bike and i know his will be the same.

if we take a look at the issue in it's most basic form the bike wont be stock allowing more air into the engine. So with stock fuelling the bike will be lean, so he needs to add more fueling to correct the air/fuel ratio


peace out :-)

[ducatilover]

You're giving me advice when it took you a year to turn your pilot screws?

Is your bike standard? If so, why was it too lean and where were the screws set at.

[Ultrasonic2]

im not giving you advice im telling him how it is on these carbs

No my bike isn't standard ( my avatar isn't actually my bike but it looks the same) and when i got it the screws were at 3-3/4's out standard is 2.5

Part of the reason why it took so long is i posted my issue here and got sent in completely the wrong direction which wasted HEAPS of time. i eventually realised that i knew more about these carbs than the people posting ( which is understandable since i have taken it apart a million times now) so there was little point posting anymore. i have dome more than just change the pilot screws by the way

Also i had other things to do. Also i had other carb issues which was affecting things and making life complicated.

[ducatilover]

Are you running CVK carbs or flat sides?
3 to 3.5 turns is miles out and far too rich, unless you're running no airbox on CVK carbs.
Interesting really, I'd like to know more about this.

[Ultrasonic2]

oh i agree that over 3 is to much and adding all that and much more seems to have been a reaction to one of the issue i was having that was performed by one of the previous owners.

ignoring performance related issues for now.

When the stock turns of 2.5 were applied to the bike, when i would pull up to the lights the bike wouldn't idle right it would stay real high like 3000 rpm ( can't remember the exact rpm ) after i while it would come down

Now if i put the turns all the way backup the bike was fine. Now interestingly someone on this forum had the same od idling issue on the same bike and said it was resolved by increasing the turns out. However that of cause mean't that at low RPM the bike was to rich. People rightly said that i shouldn't use the screw as a means to greatly increase the richness of the bike. but at this point what was i supposed to do, having a overly rich bottom end was better than idling at 3000rpm at the lights and the bike was SOO much slower at the stock turns out.


The cause of this issue ended up being from old seals on the carbs over flow. unlike alot of bikes the over just doesn't go to open air it goes to a valve which based on X vaccume would go back to the air box or to free air and possibly blocked off ( can't quite remeber ). I think all this is because of the air ram affect.

Once coming up with a plan on how to fix this cos you can't get the parts anymore i could then run the bike at 2.5 turns out but now i had the opersite problem where the bike would nolonger idle it would eventually die. i logically thought that there must be a problem with the valve. Since i'd already removed it in the past and had piped it up to were i could play with it while riding and seeing the affect of blocking it or going to free air and what not.

i did not consider at the time that the bike could be to lean cos everyone was telling me that the bike must be rich cos it bogs down when you crank the throttle open but was fine when i rolled it on slowly. so at this stage i got used to holding the throttle open at the lights.to be honest it just became normal to me

Now we come to everyone telling me the bike was rich. In hinsite it seems ridiculous to assume the bike is rich when it wasn't sock. but i listened to the people on the forum. Now I was quite aware that in my opinion increasing the the turns made the bike faster without a doubt across all rpm or load. but how could this be since everyone was telling me it was only for the first 1/4 throttle So i though this must be a issue i broke the carbs down and cleaned them a million times with my ultrasonic clean but this had no affect on anything. i started putting pipe cleaners in every hole to see if there was a blockage or anything but all seemed to be the same. so maybe something was missing from my carbs as i knew they had been played with before me. but nothing i got the service manual and the parts manual from redbarron and everything was as it should be. yet when i increased the turns out it got faster. The light eventually came on that there was nothing wrong with the carbs in THIS respect and it is IMPOSSIBLE for the fuel to stop flowing as long as the float height was correct. If you look at cut aways of these carbs you soon realise that it is impossible for the fuel to stop flowing there is no valve or door that shuts as long as the float height is right the fuel CAN NOT stop flowing through this circuit. So while people yas it does the first 1/4 of the throttle they are correct that it is the major factor but it simply doesn't stop at just over 1/4 it continues to add fuel through the whole rang because nothing is or can stop it.

249860
249861


Realising this didn't make me realise though that the bike was simply lean though. That light came on later and seems pretty obvious now.
Increasing the main jets allowed me to have a richer raito without crazy turns out.

At this point the screws were still at a stock positions and it still couldn't idle as it would die. increasing the turns has allowed the bike to idle as it should. it also increased pickup at low throttle positions

However the whole reason why i started to investigate my carb issues still remained, which was if you crank the throttle fast it would die but eventually spring back to life. Everyone was of coarse saying it was to rich. Now i couldn't understand how the fueling could be right at pretty much all throttle positions yet die when if i cranked it faster. The light came on when i found out what an accelerate pump does on a carb with out a slide and why it does it. No i obviously don't have a pump but it explained that with a quick throttle moment the bike could / would be lean. now i investigated how this could possibly happen on a bike with a slide and the obvious answer ( retrospectively ) was float levels. When you crank the throttle the level will drop and the jets dont get any fuel but if you hold it long enough the bike eventually fills the bolls up again and your away again.


SO i had 3 major issues which all affected each other but i of corse only thought i had one issue which made fixing it very hard

[ducatilover]

Very interesting reading mate, I've never happened across CV's, or any carb for that matter that have no float valve or fuel level control of any sort, the idea to leave it out is simply stupid. Are they not Keihin CVK32s or something of similar vintage?

This image suggests there are valves and seats that the float cuts off, 249879 the only reason the floats are there is to close the valve and stop the fuel flow to the carbs. Your bike won't run for very long without the needles. 249880


According to the diagram/my eyes you posted your pilot screw is on the opposite side to most CVK carbs, that means it's turn in to be richer, out to be leaner.
Whereas, this has idle screws in the normal CVK position 249878, just like the ones on my 600 and the 400 ones I have on my shelf, so in = lean and out = rich. A bit confusing, what model carbs do you have? I'd like to do some research into this incase I have to spend time on a ZXR

Being a modified bike doesn't always mean leaner, my ZZR600 is running 138 main jets when it had Neptune cans and a foam filter, standard jetting is 142.

What were the floats set at, have you had the carbs properly balanced and also set up on a flat plane to ensure they're sitting even?
How about the needles, were the needles checked for wear and the seats? How is the coating on the slides? (unless you have horrible plastic slides)
This is quite fascinating :yes:
It sounds as if someone previous to you had fucked with them without knowing what they are and how delicate carbs are.

[Ultrasonic2]

Very interesting reading mate, I've never happened across CV's, or any carb for that matter that have no float valve or fuel level control of any sort, the idea to leave it out is simply stupid. Are they not Keihin CVK32s or something of similar vintage?




to clarify i haven't taken any parts out and there isn't any missing parts. i at one point i investaged to make sure there WASN'T any missing parts or that someone had put the wrong parts in.

The website that seems to have everything right would tend to agree that if you just change the muffler this can result in you requiring to reduce the jets. and logicically if the fuelling was correct priour to the muffler change then you have reduced the bikes power as a result of reducing the jet sizes. But i'd personally rather not comment on someone elses bike knowing nothing about it.

The needles are fine and i have horrible plastic slides.
i have CVk's just like the pic you got from "dir ty Girl" so out is richer i posted those pic in relation to the pilot screws always being on rather than anything else

I just hope that people take away from reading this is that pilot screws dont stop at x point this also applies to the other jets there is no magical stop point. Im not going to be stupid enough to say this is the case for all carbs but the blanket statement that the jets stop at 1/4 or what ever in all cases is wrong. For anyone who disagrees i challenge them to find the little door or what ever that slam shut at just over 1/4 and another one that opens the next sage on THESE carbs.
(By the way this is not directed at you Ducatilover but the community as a whole)


im glad your finding it interesting. i certainly have

[Ultrasonic2]

in retro spect i have found this site very use full
http://www.hondanighthawks.net/carbhelp.htm

An this link from the same site seems to be very good at explaining how a carb like mine works
http://www.hondanighthawks.net/carb14.htm

249887

[ducatilover]

to clarify i haven't taken any parts out and there isn't any missing parts. i at one point i investaged to make sure there WASN'T any missing parts or that someone had put the wrong parts in.
Good, but, the ZXR carbs I posted had a fuel level control system like all other CVK Keihin carbs, floats, needle (or plunger if you may) and a seat.

The website that seems to have everything right would tend to agree that if you just change the muffler this can result in you requiring to reduce the jets. and logicically if the fuelling was correct priour to the muffler change then you have reduced the bikes power as a result of reducing the jet sizes. But i'd personally rather not comment on someone elses bike knowing nothing about it.
Dynojet kits are 134 main and 138 for high flow filter/mufflers, they're probably on to it too. FactoryPro kits are the same. It's not all about a big jet size, changes in VE result in different bowl pressures, different bowl pressures can be quite confusing. Dyno figures for an a-typical ZZR600 with a dynojet kit running a K&N foam element and 4-2 free flowing pipes are several HP more than when standard (same day, same dyno). Don't be fooled into thinking bigger is always better. :yes:


The needles are fine and i have horrible plastic slides.
i have CVk's just like the pic you got from "dir ty Girl" so out is richer i posted those pic in relation to the pilot screws always being on rather than anything else So we're on the same page here, pilot screw before butterfly = turn in to stop fuel flow, out for more. :D


I just hope that people take away from reading this is that pilot screws dont stop at x point this also applies to the other jets there is no magical stop point. Im not going to be stupid enough to say this is the case for all carbs but the blanket statement that the jets stop at 1/4 or what ever in all cases is wrong. For anyone who disagrees i challenge them to find the little door or what ever that slam shut at just over 1/4 and another one that opens the next sage on THESE carbs.
(By the way this is not directed at you Ducatilover but the community as a whole)
The pilot screw should have a negligible effect on the top end fueling, I tried richening up the mixture on the dyno on my VT250 by doing so as I had run out of jet sizes and didn't want to go spend more on dyno time. Made bugger all difference on the gas analyser and I had to go up a jet size, exactly the same fundamentals as your carbs too. But, I can see that your small 4cyl will be more likely to respond to a pilot screw adjustment in the top end given that the bore on the pilot circuit is very similar VS the smaller combustion chambers, I can now see how it could make a difference, I do want to try it on a small 4 cyl though to feel this difference. It hasn't worked like that on any of my bikes, it's only improved the idle and very low RPM fueling.
I try not to be too arrogant :bleh: and not all advice is sound here, I'm more than happy to learn more though.



im glad your finding it interesting. i certainly have It's very interesting, I need to spend more time on these little 4cyl beasts.


in retro spect i have found this site very use full
http://www.hondanighthawks.net/carbhelp.htm

An this link from the same site seems to be very good at explaining how a carb like mine works
http://www.hondanighthawks.net/carb14.htm

249887
Great websites there mate, interesting recap on my (not so great) carb knowledge.

Just out of interest, what jet sizes are you running (pilot and main) compared to factory?
The plastic slides can be horrible to work with, are there any replacements available? Because, they can cause a multitude of problems. I have a set of 34mm or 32mm Keihin carbs here that have proper slides and are completely fresh inside with a zillion jet sizes, would be interesting to try them on a 250 (they're off a 400)

[Ultrasonic2]

yeah i wont claim to know anything about the ZZR so i will leave that up to you.

I would also think that the pilot screw would have more of an affect on a little bike. logically adjusting the pilots will affect lower throttle positions so the bike may feel faster but ultimately at full throttle on a dyno it may make little difference. you certainly couldn't use the pilot screws inplace of adjusting the main jets

I know my bike still isn't perfect in fact im taking the bike apart on friday again.

Currently the jets are 130-132 ( stock is 122 125 ) it was still defiantly lean with 125-128's but it my be a bit rich at 130-132 what really interests me is why it has different sizes of jets it would seem most people when jetting go for all 4 the same. i haven't done enough research on this topic. whats your thoughts on this topic ?

I have spoken to a few others with simalar mods and they recon all 130's is the way to go but im a little reluctant

As for the bottom, that was taken care by the pilot screws. now i realise that's not the best way and i problaby should change the other stuff too but at the moment im still focusing on my other issues

Where in nz are you ? im in Pakuranga Auckland and this is my 3rd 4 cylinder 250 now

oh the carbs are CVK-D30 and i haven't looked into replacing the slides i assume they will be expensive and pretty much the same anyway

[ducatilover]

yeah i wont claim to know anything about the ZZR so i will leave that up to you.

I would also think that the pilot screw would have more of an affect on a little bike. logically adjusting the pilots will affect lower throttle positions so the bike may feel faster but ultimately at full throttle on a dyno it may make little difference. you certainly couldn't use the pilot screws inplace of adjusting the main jets

I know my bike still isn't perfect in fact im taking the bike apart on friday again.

Currently the jets are 130-132 ( stock is 122 125 ) it was still defiantly lean with 125-128's but it my be a bit rich at 130-132 what really interests me is why it has different sizes of jets it would seem most people when jetting go for all 4 the same. i haven't done enough research on this topic. whats your thoughts on this topic ?

I have spoken to a few others with simalar mods and they recon all 130's is the way to go but im a little reluctant

As for the bottom, that was taken care by the pilot screws. now i realise that's not the best way and i problaby should change the other stuff too but at the moment im still focusing on my other issues

Where in nz are you ? im in Pakuranga Auckland and this is my 3rd 4 cylinder 250 now

oh the carbs are CVK-D30 and i haven't looked into replacing the slides i assume they will be expensive and pretty much the same anyway

That's a HUGE step in jetting for a 250! They reason to run cylinders two and three richer is for cooling, there isn't as much cooling in the middle of the block and your intake valves are hotter and so on and so forth, the richer mixture burns colder.

I'm near Palmerston North, I had two 250's but got sick of the complete lack of power :bleh:

D-30's? So they are scaled down versions of my 400 ones and also the 600 ones.
How were you judging that it's lean?
Are you running it without an airbox?

[Ultrasonic2]

That's a HUGE step in jetting for a 250! They reason to run cylinders two and three richer is for cooling, there isn't as much cooling in the middle of the block and your intake valves are hotter and so on and so forth, the richer mixture burns colder.

I'm near Palmerston North, I had two 250's but got sick of the complete lack of power :bleh:

D-30's? So they are scaled down versions of my 400 ones and also the 600 ones.
How were you judging that it's lean?
Are you running it without an airbox?

Well the jetting was in line with the others running similar mods on the same bike. and is inline with the website. i haven't bothered to upgrade cos when properly running they are as good as the big twins ( excluding ducati ) mind you all of them were a huge deal to get running perfectly.

As for the higher jets in the middle that was the theory i thought behind them too which then doesn't make scene that you'd put 4 the same in when jetting.

As for what lean or rich it's largely based on seat of my pants and since i ride the bike everyday im very familiarly with it. ultimately it will need to find it's way to a dyno but that cost real money. At this stage i feel it's easy to tell the flatness of this lean bike.

i dont run a air filter . not even on my cars they are just pointless horses power re-stricters when i took it out it didn't appear to affect any of my issues at the time but that feels like a life time ago now

[ducatilover]

Well the jetting was in line with the others running similar mods on the same bike. and is inline with the website. i haven't bothered to upgrade cos when properly running they are as good as the big twins ( excluding ducati ) mind you all of them were a huge deal to get running perfectly. Interesting to see you're running larger jets than all 3 of my 400's have been lol that's mad.
What's as good as a big twin? A 250 sure isn't.


As for the higher jets in the middle that was the theory i thought behind them too which then doesn't make scene that you'd put 4 the same in when jetting.
That's why they are like that though. It helps cool the motor, it's not for maximum power. A lot of old V-twins run larger rear jets as the rear cylinder is out of the airflow.
My ZZR400, CB400 and GPZ400R (I keep buying 400's, no idea why) all had larger jets on 2 & 3. Strangely, my ZZR600 runs one size all round.


As for what lean or rich it's largely based on seat of my pants and since i ride the bike everyday im very familiarly with it. ultimately it will need to find it's way to a dyno but that cost real money. At this stage i feel it's easy to tell the flatness of this lean bike.
Not the ideal way.
Hove you done plug chops to see how rich/lean it is?

i dont run a air filter . not even on my cars they are just pointless horses power re-stricters when i took it out it didn't appear to affect any of my issues at the time but that feels like a life time ago now
You have CV carbs, they rely on airbox pressure (airfilter helps control this) to work correctly. If you want to run no filter and fuck your engine, get flatsides. If you get it dyno'd one day, do me a favour, try it with the air filter in and full airbox/ram air (assuming you have it) and look at the results.

[Ultrasonic2]

big harley twins are simple to beat even on paper my power to weight ratio is better than their's (the cases i have seen) and my old mans harly mates i get respect from.

Plug chop isn't practical on this it would take ages to get them out well thats my "op"

The air box and air ram im still running i haven't tired it with the air filter in lately but i doubt it will make a difference to my issues. I am completely aware that people say dont take the air filter out cos it will stuff up the fuelling which is logical and i wouldn't recommend people to take it out if the bike is fine but since the carbs where already up the creek i thought why not im already taking it apart every week cos it's carbs have issues. in my case i dont believe removing the air filter was the cause of anything since it had these issues before i removed it.

As for jet sizes you would think they would be smaller than the ZXR400 wouldn't you? but the zxr400 of the same year has MILES smaller jets for some reason . ie it has 95's where mine stock has 122-125 ( yes that's what's in the manual ) interesting that it appears to have all at 95's instead of having bigger middle jets

other interesting things, is the main air jet, needle jet and pilot jets are the same on the bikes leaving the started jet and pilot air jet the only differences and of those both are smaller on the 400

The 250 runs cvkd30 V cvk-d32 basically the 400 is 2mm bigger i think


http://www.zxrworld.co.uk/Manuals/L%20Model/ZXR400%20L%20Chapter%202.pdf

[ducatilover]

Depends on what model Harley. I've ridden a hotted up 883 Sporty that'll rape any 250 4 stroke I have ridden. I've seen many a Harley leave CBR/ZXR in the dust (before a corner...) a 4 stroke 250 is by no means fast. I hate them with a passion though (Harleys), I'd rather a smooth Jap bike :banana:


My CB400 ran 95/98 standard jets in D-32s, my ZZR400 has the D-32 carbs and they have 124s in them
It goes to show, it's not jet size.
The bowl pressure has a huge effect on what size jets you need, maybe that's why you need such large jets?

Those 400 carbs in that manual are the same as the ones on my shelf.
I still fail to see how you have a float and no needle/seat to stop fuel flow in to the bowl? How is the fule level regulated then?

[Ultrasonic2]

249939

This thing (883 cc). hell no my work mate has one of these i literally raced him off at the lights today
I can undertand your point of view if you've ridden one of the single or twin 250's or the late 90's 4's. mine is the lost powerful of the lot due to regulations, as you probably know. but lets not get into this fruitless augment.

Your probably right about comparing jets between bikes it seems a waste of time. Still it's interesting,

Now you might be on to something about the pressure. from memory the 400 has a fuel pump which the 250 doesn't but dont quote me on that

EDIT just checked and yes the 400 has a fuel pump

oh and i have no idea what you mean by this ? I still fail to see how you have a float and no needle/seat to stop fuel flow in to the bowl? How is the fule level regulated then?

there is a little seat in there with a mesh filer in there it's not in dirty girls pic's

[ducatilover]

Been there and ridden them all mate, and I have ridden an 883 that would lick any 4 stroke 250 I've ever ridden. A standard cammed 883 would be beaten when the revs get up there by nigh on anything, the 883 is lucky to make as much RWHP as a 400 4cyl.

The ZXR400 had a pump, my ZZR400, CB, GPZ haven't got pumps. It'd make a difference, yes, but the pumps are still very low pressure. It's the air venting to the bowls that'll do it. What are your bowl vents like anyway?

I thought you said earlier that you have no float valve and seats in your carbs?

[Ultrasonic2]

I thought you said earlier that you have no float valve and seats in your carbs?

no i never said that

It's the air venting to the bowls that'll do it

Not a 100% on what you mean by that

[Ultrasonic2]

ok well lest talk numbers now
the 1200cc nighster makes 61hp and weights 254kg 0.240
my bike makes 43 and weight 141kg power to weight of 0.304

So in theory i will beat it as i have a greater power to weight ratio. i of course dont need to beet it to gain respect from the 1200cc rider. So when im up against the 883 i have No problems seeing it off. It's important to clarify that im talking about 0 to about -120ks

one of the interesting things about bikes is as the size increases they seem to be geared up more and which is counter productive. even my to 250 was geared up to much. ( i geared it down) these massive 4 can do 300km's but who cares by gearing them to beable to achieve that you've decreased their slower speed acceleration

http://www.motorcycle.com/specs/harley-davidson/standard/2009/sportster-reg/1200-nightster/detail.html

http://www.knfilters.com/dynocharts/63-1126_dyno.pdf

[ducatilover]

no i never said that

It's the air venting to the bowls that'll do it

Not a 100% on what you mean by that
Your bowls have air venting. If your bowls are incapable of venting, you'll have problems.


ok well lest talk numbers now
the 1200cc nighster makes 61hp and weights 254kg 0.240
my bike makes 43 and weight 141kg power to weight of 0.304

So in theory i will beat it as i have a greater power to weight ratio. i of course dont need to beet it to gain respect from the 1200cc rider. So when im up against the 883 i have No problems seeing it off. It's important to clarify that im talking about 0 to about -120ks
Torque to weight, you have 24nm.....
I'd say a 1200 Sporty will have a ZXR250 up to 120-130 or so. Or at any speed up a hill....in to a head wind...
I don't care either way, I've ridden Harleys that will dispose of a 250 4cyl. Which, let's be fair, is nothing special. A Harley is not designed to be quick and a ZXR250 is certainly not quick.


one of the interesting things about bikes is as the size increases they seem to be geared up more and which is counter productive. even my to 250 was geared up to much. ( i geared it down) these massive 4 can do 300km's but who cares by gearing them to beable to achieve that you've decreased their slower speed acceleration

http://www.motorcycle.com/specs/harley-davidson/standard/2009/sportster-reg/1200-nightster/detail.html

http://www.knfilters.com/dynocharts/63-1126_dyno.pdf
Your ZXR should be ideally geared to a true 200k, that's the realistic max you'll see out of one, 205 if you're very, very lucky (been there, done this)
I think the standard gearing was a theoretical 223 or so, not including wheel slip etc. They'll never manage that.
The bigger bikes can afford to be geared longer, better economy and they have enough torque to push the gearing. My ZZR is geared nicely, sits at 5000 rpm at 100, it'll overtake anyone up a hill at those revs. Sadly a 250 won't.

Will you let us know how the next carb strip down goes?

[Ultrasonic2]

Yeah it better not rain on Friday night so i can take it apart. im gonna adjust the float levels or at least know for sure what they are now. im gonna make a measuring device cos last time i tried with a ruler and that was a bit vague

oh the 250 has a jap 180 limiter

[ducatilover]

Yeah it better not rain on Friday night so i can take it apart. im gonna adjust the float levels or at least know for sure what they are now. im gonna make a measuring device cos last time i tried with a ruler and that was a bit vague

oh the 250 has a jap 180 limiter

Use verniers, it's always worked for me. They're cheap to buy and pay for themselves time and time again.
I'd check your plugs to see how they're burning, and go from there :yes:

I've never ridden one with a 180 cut out.

[Ultrasonic2]

right carbs have been off and back on again

manual says the float height should be 13mm +-2mm

They were at 14mm so i put them down to 11 mm

I also went one step down all round to 128-130 again after running the 130's to 132's for a week.

The bike was much worse. im disappointed but at the same time it counts the float height out as being the issue and bringing it back to just simply being to lean. Now most people would say you need to put a washer under the needles and i would tend to agree but when i tried it i couldn't even get down the street as i couldn't get the throttle much past idle. i could and probably should re rest this now but that is a big deal having to take the crabs off twice in a row.

I could increase the Jet sizes which would probably pretty much solve the problem but i would think the bike would be super rich by then. i could possible add more via the pilot. i dont know yet. What i do know is the dip is because it is to lean with out a doubt, so i guess i have achieved something.

Thoughts opinions anyone

[Ultrasonic2]

Right went back to 2.5 turns out with 0.75mm washers under the needles. jets are 128-130
epic fail, will die when you open the throttle

Went to 3.5 turns out and 130-132 jets with no washers
Fail was to rich

Now im gonna try 2.5 turns out and 130 -132 last week i had it at 3 turn out which my have been sightly to rich down low and im wounding since the float height change maybe 2.5 turns out will be fine

[Ultrasonic2]

Right performed the above and it's still rubbish. At this stage i just need it going again so will probably change the float height' it's all a bit disappointing it's possible changing the float fixed the issue at 9k but it's created a whole bunch more that are worse. i kinda want to change the float height to 15mm now. but probably shouldn't my wife would explode if i had to take it apart again. if changing the height did make the issue at 9k worse or better im not sure what i can really do about it anyway.

humm myabe i't try 15mm

What i think would be very interesting would be to put the stock jets back in and leave the float height as i have it now 11mm but im kinda over it again for a while

[Ultrasonic2]

right so i put it back to how it was last week but unfortunately it's still poked and im not sure why ? ill have to take it apart tomorrow again to see if i've picked up a blockage some how or some thing. what this does mean is everything i've said since and including changing the float level is probably not true .. orr

what a epic waste of time

[ducatilover]

right carbs have been off and back on again

manual says the float height should be 13mm +-2mm

They were at 14mm so i put them down to 11 mm

I also went one step down all round to 128-130 again after running the 130's to 132's for a week.

The bike was much worse. im disappointed but at the same time it counts the float height out as being the issue and bringing it back to just simply being to lean. Now most people would say you need to put a washer under the needles and i would tend to agree but when i tried it i couldn't even get down the street as i couldn't get the throttle much past idle. i could and probably should re rest this now but that is a big deal having to take the crabs off twice in a row.

I could increase the Jet sizes which would probably pretty much solve the problem but i would think the bike would be super rich by then. i could possible add more via the pilot. i dont know yet. What i do know is the dip is because it is to lean with out a doubt, so i guess i have achieved something.

Thoughts opinions anyone
11mm on your floats will make it richer. The higher the number, the leaner it becomes.
I recommend going back to exact factory settings, then twiddle from there.


Right went back to 2.5 turns out with 0.75mm washers under the needles. jets are 128-130
epic fail, will die when you open the throttle

Went to 3.5 turns out and 130-132 jets with no washers
Fail was to rich

Now im gonna try 2.5 turns out and 130 -132 last week i had it at 3 turn out which my have been sightly to rich down low and im wounding since the float height change maybe 2.5 turns out will be fine


Right performed the above and it's still rubbish. At this stage i just need it going again so will probably change the float height' it's all a bit disappointing it's possible changing the float fixed the issue at 9k but it's created a whole bunch more that are worse. i kinda want to change the float height to 15mm now. but probably shouldn't my wife would explode if i had to take it apart again. if changing the height did make the issue at 9k worse or better im not sure what i can really do about it anyway.

humm myabe i't try 15mm

What i think would be very interesting would be to put the stock jets back in and leave the float height as i have it now 11mm but im kinda over it again for a while


right so i put it back to how it was last week but unfortunately it's still poked and im not sure why ? ill have to take it apart tomorrow again to see if i've picked up a blockage some how or some thing. what this does mean is everything i've said since and including changing the float level is probably not true .. orr

what a epic waste of time


What you want to do, is set floats, jets, needles to factory. Put the airfilter in.
Get the top end correct, find a jet that pulls well right up top, do not worry about the lower end.
If it pulls good, time to do the needles.
If it bogs down or feels wet at 8000-10,000rpm, lower the needles, if it has a big flat spot, raise them .5mm at a time.
Once that's sorted, get your midrange done, 4000rpm and up is where your floats come in to play, so too rich means you want to lower the float height (bigger measurement) Do it in 1mm increments, I know it takes ages to get right, but that's life.
Once that's done, you can set the idle, you may have problems down low using the factory pilot jet, but I doubt it.
If you need bigger pilots, I might have some here.


This is how I've always done my carbs, it's how Factorypro and Dynojet and all the carb nuts tell you how to do it.

One very important thing Only change one thing at a time.

That's all just off the top of my head, my carb book has gone A.W.O.L

[Ultrasonic2]

Right fixed my issue

im not sure when it happend or why but it's fixed now and thats all that matters and im oddly happy that the bike is just like it was last week

The issue i had was i had petrol in the overflow . now i know you'll all be saying thats the point of the over flow but not on this bike as mentioned before the overflow goes uphill to a valve that then has 4 pipes connected to it .im not going to go into the workings of this except to say it has a huge affect on the fuel of this bike. now no matter what happens at this valve if there is fuel in this line it has to go up hill even after the valve. Any way there was alot of fuel in this line that was completely stuffing up the fuelling of the carbs the bike made the most odd sound when this issue existed now i dont know if the fuel got in there because or the float height adjustment of because of the way i took the carbs off at one stage. i actually believe it was because of the way i removed the carbs that one time. anyway once i tipped the fuel out the problem went a way after a few minutes of riding.


As for the issue im trying to fix i should stop pissing around and actually fix it by jacking up the needle height. The only problem is where do i find 3mm .2 shims from ?

and for the main jets i probably should just do what the others have run which is all 130's( not that i like that thought) i know 125-128's is to lean and i believe 130-132 is to rich. I guess really i need a dyno to answer the question truthfully :-)


anyone know where i can get shims from ?

[ducatilover]

That's quite interesting, good to hear you have it sorted!:niceone:

Ring around engineering shops, I've always used washers that are .5mm thick. :cool:



I'd really like to see pics of your carbs, I've never seen an overflow running up into a valve, is the overflow running higher than the float height?

[Ultrasonic2]

Here's a pic for you. form when i spent ages investigating this valve

http://www.tecpeltier.com/download/file.php?id=138&mode=view


i only have .75 shims and these carbs are pretty sensitive so that's why i'd like to get. 0.2mm shims. i still can't make up my mind on what jets to run


oh and here's a pic of my bike

http://www.tecpeltier.com/download/file.php?id=215&mode=view

[ducatilover]

Doesn't make sense to me lol

Very nice looking ZXR!



Try doing the steps I posted up before.

[Ultrasonic2]

um yeah after having the carbs off like 7 times this weekend i wont beable to play with it next weekend. but thats ok it will give me time to find some shims

Man i wish the original guy would post again

[ducatilover]

If you want to get it working properly, you need to do what I've posted dude.

[Ultrasonic2]

What you want to do, is set floats, jets, needles to factory. Put the airfilter in.
Get the top end correct, find a jet that pulls well right up top, do not worry about the lower end.
If it pulls good, time to do the needles.
If it bogs down or feels wet at 8000-10,000rpm, lower the needles, if it has a big flat spot, raise them .5mm at a time.
Once that's sorted, get your midrange done, 4000rpm and up is where your floats come in to play, so too rich means you want to lower the float height (bigger measurement) Do it in 1mm increments, I know it takes ages to get right, but that's life.
Once that's done, you can set the idle, you may have problems down low using the factory pilot jet, but I doubt it.
If you need bigger pilots, I might have some here.


This post ?

yeah i agree with that i think and im onto changing the needles
just ordered 20x0.1 20x0.2 20x0.3 3mm shims for $14.10 delivered thats from hongkong Gota love the internet


My gut thinks 0.4 will be the right height with 128-130 jets but we will see

[ducatilover]

What you want to do, is set floats, jets, needles to factory. Put the airfilter in.
Get the top end correct, find a jet that pulls well right up top, do not worry about the lower end.
If it pulls good, time to do the needles.
If it bogs down or feels wet at 8000-10,000rpm, lower the needles, if it has a big flat spot, raise them .5mm at a time.
Once that's sorted, get your midrange done, 4000rpm and up is where your floats come in to play, so too rich means you want to lower the float height (bigger measurement) Do it in 1mm increments, I know it takes ages to get right, but that's life.
Once that's done, you can set the idle, you may have problems down low using the factory pilot jet, but I doubt it.
If you need bigger pilots, I might have some here.


This post ?

yeah i agree with that i think and im onto changing the needles
just ordered 20x0.1 20x0.2 20x0.3 3mm shims for $14.10 delivered thats from hongkong Gota love the internet


My gut thinks 0.4 will be the right height with 128-130 jets but we will see

That's the one man.
I get a shit load of parts from HK, go eBay!

Are you pulling the plugs when you change the carb settings?

[Ultrasonic2]

That's the one man.
I get a shit load of parts from HK, go eBay!

Are you pulling the plugs when you change the carb settings?

no i haven't been pulling the plugs that takes to long. But really at this sage im no where near fine tuning it. I'll fix all my "issues" then fine tune it.

any idea what a dyno with gas analysis costs ?

[ducatilover]

no i haven't been pulling the plugs that takes to long. But really at this sage im no where near fine tuning it. I'll fix all my "issues" then fine tune it.

any idea what a dyno with gas analysis costs ?

Most of my tuning has been almost spot on before dyno time, it's do-able with carbs. Just do it once and properly.
Also, there's no point if you haven't done your valve clearances (same goes for balancing) or if you have cam chain stretch (throws your valve timing out a bit.)

It should go -
Valves/cam timing.
Balance carbs.
Tuning.
Skids.

$75 down here last time I did it, probably a bit more in Auckland?

[Ultrasonic2]

i replaced the cam chain and tensioner 3 months ago and the spark plugs and had the valves re shimmed

ooooo i just found a unrestricted CDI (for the hp limit) for my bike. i want it

i haven't found them before

[ducatilover]

Is the CDi an SP model one? If you find any 250SP parts, snap them up.
Yours is before the 40hp law isn't it?

Good that you've done the cam chain, it's a weak point on the ZXR

[Ultrasonic2]

yes mines limited to 45 by law

[ducatilover]

I never knew they were limited to 45, I know they went to 40 in late '93 (from memory)
What kind of power do you expect with a de-restricted CDI? I'd love to get a ZXR250SP, but they're insanely rare, almost non-existant :weep:

[Ultrasonic2]

yeah that why the ZXR CBR and FZR of the same age all make the same hp of a rather round 45hp . by the way i have owned all of them now

[ducatilover]

I haven't owned any, but I've ridden one of each Fizzer250, and a million MC19's, MC22's and ZXRA&C models.
My personal choice was the MC22, I just can't turn them down.
I think the 3LN3 onwards Fizzer looks absolutely hot and I'd love to have one, just to look at.
The ZXR never seemed to suit me, great bike though, no doubt about that. I'd own one, but I'd rather throw a leg over a CBR.

I've never lined them up together though, but most seem to make 34-36hp at the wheel, so the biggest difference would be gear ratios I suppose.

What's your pick of the lot?

[Ultrasonic2]

Well I have had an interesting experience with them so I wouldn’t pic a winner
The first one was a fzr and it handled really well but wasn’t that fast.in the end it had a rusty tank and forks so sometimes you had no brakes .
Then I got the cbr mc19 it was mind blowingly fast that it was actually slow. Dyno’d it and it got more and 50hp at the wheel which seemed to shock redbaron but all the power was over 18k which mean it was SOOOO slow at normal rpms. If I wanted to pass anyone on the moterway I would have to change down like 3 gears. Off at the lights it kind of sucked cos I had to get to the 18k. on a club ride it was also kinda crap cos I didn’t want to ride at 18k + for 6 hours cos I was afraid it would explode. SO it was fast but 99.9 % of the time the power was unusable and was ultimately slow in traffic. The bikes handling wasn’t as good as the FZR too. The mc19 doesn’t have adjustable shoks which I think was part of the problem. It may have just needed new shock oil. It doesn’t matter now as it died.

ZXR handles really really well and currently isn’t as fast as the cbr and probably never would be. Im not going for peek power this time cos I learnt my lesson on that one. Im more interested in at acceleration at 8-12k which is where I ride

[ducatilover]

Well I have had an interesting experience with them so I wouldn’t pic a winner
The first one was a fzr and it handled really well but wasn’t that fast.in the end it had a rusty tank and forks so sometimes you had no brakes .
Then I got the cbr mc19 it was mind blowingly fast that it was actually slow. Dyno’d it and it got more and 50hp at the wheel which seemed to shock redbaron but all the power was over 18k which mean it was SOOOO slow at normal rpms. If I wanted to pass anyone on the moterway I would have to change down like 3 gears. Off at the lights it kind of sucked cos I had to get to the 18k. on a club ride it was also kinda crap cos I didn’t want to ride at 18k + for 6 hours cos I was afraid it would explode. SO it was fast but 99.9 % of the time the power was unusable and was ultimately slow in traffic. The bikes handling wasn’t as good as the FZR too. The mc19 doesn’t have adjustable shoks which I think was part of the problem. It may have just needed new shock oil. It doesn’t matter now as it died.

ZXR handles really really well and currently isn’t as fast as the cbr and probably never would be. Im not going for peek power this time cos I learnt my lesson on that one. Im more interested in at acceleration at 8-12k which is where I ride

An MC19 making over 50hp at the wheel? How on earth did someone manage that! I've heard of 38 in a good, full exhaust, no airbox MC22....

To be fair, any sort of peak power from a 4cyl 250 still won't be much. My 90+hp at the wheel doesn't feel stupidly fast to me.

[Ultrasonic2]

Stupidly fast was in comparison to the fzr250

yeah well in my experience their has been two problems with 400 and 250 owners

1 people bolt on parts and dont change the fueling or they come to a forum and get told a whole bunch of rubbish and still dont get the fuelling right. hardly any of them get their bike gas realized on a dyno to get the fuelling right

2 no one deals with the fundamental issue even though they agree there is a limiting factor and that is the HP limit. if you dont remove the HP limit adding bolt on parts wont make that much difference upto. im sure i'll get over 40hp on the dyno because im dealing with it's issues. fuelling and the hp limiter.


The mc22 would probably be a 40hp limited bike, that doesn't mean you can't get more than 40hp out of it though. i might point out that the 400's are also HP limited

[ducatilover]

Stupidly fast was in comparison to the fzr250

yeah well in my experience their has been two problems with 400 and 250 owners

1 people bolt on parts and dont change the fueling or they come to a forum and get told a whole bunch of rubbish and still dont get the fuelling right. hardly any of them get their bike gas realized on a dyno to get the fuelling right

2 no one deals with the fundamental issue even though they agree there is a limiting factor and that is the HP limit. if you dont remove the HP limit adding bolt on parts wont make that much difference upto. im sure i'll get over 40hp on the dyno because im dealing with it's issues. fuelling and the hp limiter.


The mc22 would probably be a 40hp limited bike, that doesn't mean you can't get more than 40hp out of it though. i might point out that the 400's are also HP limited
Got any links to info on the 45hp laws? I never knew it existed, only the 40hp law.
I'd be very, very surprised if you got 40hp on a Dyno with a ZXR, unless it's correcting it for crank HP by using the drag off the throttle to calculate the percentage of power lost, then you'll get over 40...I will put money on the dyno being set up to correct it and make a predicted crank hp rating. Otherwise you had the most powerful 4 stroke 250 I've ever heard of.
I've only ridden one 40hp MC22, the rest have been earlier with the 19,000rpm redline, restricted ones had the same rev counter as an MC19, 18,000rpm redline. I've never been on a restircted ZXR either, only A and early C models.

How is the HP limited in the 45hp ones?

BTW a 40hp 250 will generally make 32 at the wheel.
My VT250 Spada did 32 standard.

[Ultrasonic2]

Yes it is possible the dyno was calculating fly wheel hp i couldn't tell you for sure.

With out even tying i found 2 you tube videos for over 40hp at the wheels crb250's
http://www.youtube.com/watch?v=xIeIc2m5N00
http://www.youtube.com/watch?v=slNkOdFD22k

You can find over 40hp ZXR's on the net too.

And here we go on the hp restrictions prior to 1993
http://bikerpat.blogspot.com/2007/06/history-of-modern-400cc-superbike.html

like i said once you understand the bikes were limited removing the hp limiter can obviously release previously un tapped power.
But really i didn't need to post a link to the hp restrictions it just takes common scene. 3 different bikes all making the same HP, thats impossible with out some hp limiting going on. You can also clearly seeing this going on with the 4 hundreds.

peace out my friend

[ducatilover]

:niceone:

Cheers man, great stuff to read and now I'm more educated.
I am impressed (very) with those HP figures from those CBR's!

[Ultrasonic2]

i've been thinking over the past couple of nights and this is where im at

1. Slide Spring
2. Slide Diaphragm
3. Vacuum Slide
4. Vacuum Port
5. Needle Jet
6. Main Air Jet
7. Main Jet
8. Slow Jet
9. Idle Mixture Adjustment Screw
10. Throttle Plate
250820

Right so there are only 2 ways that fuel enters, this is via the Slow jet(8) and Main jet(7)

The idle mixture adjustment screw allows part of the slow jets fuel(8) though at idle and beyond. But the max fuel this can allow though is ultimately limited by the jet it's fed by the slow jet (8)

The slow jet has it's own out let to deliver is maximum fuel that it's restricted

When the engine is at full rpm and at full open throttle the maximum fuel is delivered by this circuit and it is solely based on the slow jet size. whether or not the fuel is coming from the slow jet hole or the idle mixture screw hole at the same time, because all of this fuel has to pass though the slow jet.

SO It is true that adjusting the mixture fuel will affect the air fuel raito's at low vacuum settings but ultimately at full vacuum it will have NO affect at all, as the slow jet is already delivering is max fuel whether or no it is 1 or 3 turns out

It is also true that 9 and 8 can't be stopped once delivering fuel.



Cool im having fun

[ducatilover]

Now get a gas analyser and see how much difference the idle screw makes. It's naff all over 3000rpm :bleh:


Carbs are fun things though aren't they?

[Ultrasonic2]

Now get a gas analyser and see how much difference the idle screw makes. It's naff all over 3000rpm


Carbs are fun things though aren't they?

well that was a comment on the carbs pictured. i know mine has another potential inlet . though i thought it was blocked off

i wish all carbs were the same though it would make everyone's life easier

[ducatilover]

Yours work the same as all the ones in my garage man :niceone:

[Ultrasonic2]

on the up side there really shouldn't be any problems with me running more than 3 turns out. i really want to go back to 3-1/4 3.5 out which it idled better at

[ducatilover]

on the up side there really shouldn't be any problems with me running more than 3 turns out. i really want to go back to 3-1/4 3.5 out which it idled better at
You could go up one size on low speed jet? What size are yours? I might have some floating around.

[Ultrasonic2]

#35

and it probably should be bigger. i have looked for a biker one with no luck so far

[ducatilover]

#35

and it probably should be bigger. i have looked for a biker one with no luck so far

Damn, I think the ones in my 400 carbs are 35's too. :mellow:

[Ultrasonic2]

oh well :-)

i'll put the new CDI in this weekend since i wont beable to take the carbs off

[Ultrasonic2]

i just plugged the CDI in and it doesn't work .FFS

[ducatilover]

Is it new or second hand? :no:

[Ultrasonic2]

it just cuts out at the lights every 10 minutes if i just wait 5 minutes it will work for another 10 minutes

i tried 0.3mm shims under the needles but that was no good. I will try 0.1 and if that doesn't help i dont think there isn't much i can do next. i would love to try a different tapered needle as i think that would be better than lifting it's height.

i really struggle to understand how the issue can happen.
From o - 18krpm Full throttle is fine
low throttle is fine

Cranking the throttle open below 6k is fine.
Cranking the throttle open above 10k is fine
The closer it gets to 9k the worse the problem gets.
Im still confident the bike is to lean

[Ultrasonic2]

just tried 0.1 shims but that makes the rest to rich. maybe the ultimate issue is to rich i dont know.

i give up

[Ultrasonic2]

im going to take a different approach and replace the float needles and seats and call it a day

[ducatilover]

When you are replacing the caps over the diaphragms, put a spanner under the slide to hold it up further than its normal position, this will make sure you've got them sealed correctly. Have had the same problem.

Did you do the tuning step by step as I wrote it out?

[Ultrasonic2]

no i didn't. have done that kind of thing in the past. I dont believe that is the issue

it's going to be a float needle / float height issue.

The problem last time when i changed the float height is that then made the bike to rich changing the float height may or may not have fixed the issue but now it was to rich. I probably changed the float height to much.

I really want to increase the float height ( lower the measurement) but i think i'll need to lower the needles but that is not possible as they aren't adjustable.

simply replacing the float needles may make the problem disappear

[ducatilover]

Float needles may help, I'd rebuild the carbs just because it's not very expensive and worth it.

[Ultrasonic2]

Float needles may help, I'd rebuild the carbs just because it's not very expensive and worth it.

yeah ..

i forgot to say that i lowered the float level and it made the problem worse. SO it is a float issue .

will have to wait till next month before i can aforred a rebuild kit

[ducatilover]

yeah ..

i forgot to say that i lowered the float level and it made the problem worse. SO it is a float issue .


Or the float is a contributing factor.
They shouldn't be if they're all the same, only lower them in small increments. :Punk:

[Ultrasonic2]

im seriously considering adding a fuel pump from the 400. it all costs money but i think it would be worth while to have the same fuel pressure irellevant of how much fuel is in the tank and would most probably solve the problem in a different way.

i will have to look into it but is can't be to hard to add a pump and a relay

[ducatilover]

You'll have the same pressure regardless, gravity is constant. (In my mind) :sweatdrop

[Ultrasonic2]

a fuel pump off a 400 apply about 2 psi. it doesn't really matter i've ordered new float seats and valves which im hoping will actually solve my problem. i will have to wait and see

[ducatilover]

Good luck bro :cool:

[Ultrasonic2]

Right so i got the cdi working now :-)

I have now replace the float needles and seats and am playing with float heights again. i think im close to having something close enough to right.

While changing the float needle and seats seems to have reduced the problem it still remains. the float height is at 14mm and i how i found the bike. the manual says it should be 13mm, which i have tried and 12mm but doing so only makes the problem worse. changing the float height is the only way i can think of leaning the bike out