ZXR250 - hesitation and stalls when warm

[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.





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, 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.


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 , 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
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

[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.

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.

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 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

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

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

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%...hapter%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


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]

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