I want to change the jets in my bike?

[Ultrasonic2]

I have a ZXR250 and want to change the Jets in it as it's clear it's running lean up top . the main jets are 122 and 125
1st question is. where should i get jets for it
2nd question is. what increaments shall i go up in +3's +5 +10s any ideas ? i m sure im not the first person to change the jets

Any thoughts guys

Thanks

[MSTRS]

Try lifting the needles first.
<img src=http://recaffeinated.net/bike/index_files/carb101_files/needle.gif>
This is an exaggerated view, but basically you take the needle out of the slide, move the little circlip down one groove towards the point and refit to slide. Do it to all carbs and then run the bike.
By lifting the needle, you are kind of making the jet bigger, since the taper of the needle doesn't sit as far into the main jet.

[Ultrasonic2]

i didn't take the needles out last week when i took them apart. i didn't think they were adjustable but i dont know. I im guessing i could up a washer under it to lift it up. That seems a bit dodge though?

[bogan]

iirc, the needle is good for mid range, while the jet size governs full throttle, and the slow jet is for the bottom. However changing the main jet will require you to adjust the needles anyway.

Just looking through my jet kit for the bros.
step 1) select best main jet, it'll pull the hardest a top end (will probly run rough as guts till it gets there.
step 2) set needle position (midrange upwards) gotta pull hard to the upper range when the engine is hot or cold, again low will be rough.
step 3) float height so no stumbling (missing) between 2-3k at full throttle
step 4) fuel screw....

so to come to the point of it all, does it have the original exhaust and intake? if so, you shouldn't need to re-jet unless the old ones are worn out (assuming nobody else has fucked with them), if it is different you probably need to rejet, in the above order.

[Max Preload]

I'm guessing I could up a washer under it to lift it up. That seems a bit dodge though?Not 'dodge'. But it will richen the midrange.

What actually makes you think it's lean up top, anyway?

[MSTRS]

i didn't take the needles out last week when i took them apart. i didn't think they were adjustable but i dont know. I im guessing i could up a washer under it to lift it up. That seems a bit dodge though?

I could be wrong, but most m/c needles I've seen have 5 grooves with a circlip in one of them to set the needle height. Circlip is commonly in groove 3 x factory. Mostly, the needle just drops through a hole in the slide, the circlip dictating how far. Different carbs have different ways of holding the needle down, once it's in the slide.

[ducatilover]

Spacing the needles isn't going to help if it's too lean right up top, the needle will be fully clear of the jet by then.

Why is it too lean and how do you know? What year is it? Is it a zxr250a/c? Is it restricted (93 onwards or 18,000rpm redline)

[MSTRS]

He's talking about a flat spot (or chugging) at around 4000rpm. Lifting the needles is right. At least to start with...

[ducatilover]

He's talking about a flat spot (or chugging) at around 4000rpm. Lifting the needles is right. At least to start with...

I can only see him saying it's lean up top? Have I been on a Honda so long my eyes are giving up?

[bogan]

I van only see him saying it's lean up top? Have I been on a Honda so long my eyes are giving up?

same here?? also 4000 on a zxr is closer to low than mid too init?

[schrodingers cat]

Why not take it to someone who knows this shit.
Ask them to explain what they did and why.


That way you'll learn something without all the grief.
They may also diagnose an entirly different issue.

DON'T take it to 'my mate (who sez...)'

That will be all

[MSTRS]

I can only see him saying it's lean up top?

Oh - sorry - I'm following on in this thread from discussion/s here (http://www.kiwibiker.co.nz/forums/showthread.php/104410-Engine-response-at-low-revs.?p=1129934672#post1129934672)

[bogan]

ahhh, so there is different headers and muffler, if these have been done without a full rejet it probably needs one, if they were done by somebody who doesn't know what they were doing, it probly needs a full rejet.

[ducatilover]

Dyno it with an exhaust gas analyzer up the pipe and go from there. :yes:

[paturoa]

Try this site - but may be a little too big for the two fiddy.

http://rpmware.com/tag/jet-bike

[Ultrasonic2]

you i could take it to some one and get them to do it BUT . i love to learn new things and muck about. so i figure it will be fun to do it myself and i'll have a sense of achievement . ultimately it will need to be on the dyno to get it perfect which i will in the future but for now i recon i can get it close ish by the seat of my pants

i think it's lean because
If i change the plot screws from the stock 2.5 turns to 3.5 turns i makes a MASSIVE difference. Now if the bottom is lean then the top should be too.

Other issues id like to fix is the bike chugs VERY badly around 4,000rpm and currently i have to try and avoid that rpm which is hard when i commute on it

so what are we saying ? changing the needle clip may fix the 4,000rpm issue ? and i should change the main jet and possibly the pilot / slow jet ?

EDIT

oh yeah i have a 1992 ZXR 250 c2

i've had a 1988 FZR 250 and 1989 CBR 250

MORE edits

The Needle isn't adjustable. could still washer it though

i found the pic which was making me think it's not adjustable

http://www.dirtygirlmotorracing.com/zxr/carbs-zxr-pieces-needles.gif

[ducatilover]

you i could take it to some one and get them to do it BUT . i love to learn new things and muck about. so i figure it will be fun to do it myself and i'll have a sense of achievement . ultimately it will need to be on the dyno to get it perfect which i will in the future but for now i recon i can get it close ish by the seat of my pants

i think it's lean because
If i change the plot screws from the stock 2.5 turns to 3.5 turns i makes a MASSIVE difference. Now if the bottom is lean then the top should be too.

Other issues id like to fix is the bike chugs VERY badly around 4,000rpm and currently i have to try and avoid that rpm which is hard when i commute on it

so what are we saying ? changing the needle clip may fix the 4,000rpm issue ? and i should change the main jet and possibly the pilot / slow jet ?



I have thought the same, but, with a bike like the ZXR you really want to see what is happening.
How are your coils/ leads/plugs?
Any air leaks?
You pilot screws should only adjust the idle bypass ports in the carbs, letting more air in/restricting air, this should take care of your throttle until 3-4krpm.
Space the needle height up do this in increments of 0.5mm at max, if it cures the problem, you are lucky.
If not, jetting will be necessary or.... the carb slides are opening at the wrong rate, not likely as they will have a soft srping and Vacuum operated.
Now, if you need to jet, buy a variety of jets, I doubt you will need bigger than 130s for numbers 2/3 cylinders. Buy in the smallest steps you can.

Are your headers home made? Has any port work been done? Are the headers longer or shorter to the collector(s)/ Y pipe?
What kind of air filter is it?



Does the bike ever backfire when you back off the throttle?

[Ultrasonic2]

Are your headers home made? Has any port work been done? Are the headers longer or shorter to the collector(s)/ Y pipe?
What kind of air filter is it?



Does the bike ever backfire when you back off the throttle?


Dont know the answer to your questions as i bought it like it is (no back fires though ) and i've had it apart a million times mainly to fix the 4,000 thing. which i though was a blocked jet then and air leak then i decided to put the pilot screws back to stock and now it's put me on the track of the carberation/jetting being wrong, which is where we are now

[ducatilover]

Dont know the answer to your question as i bought it like it is and i've had it apart a million times mainly to fix the 4,000 thing. which i though was a blocked jet then and air leak then i decided to put the pilot screws back to stock and now it's put me on the track of the carberation/jetting being wrong, which is where we are now

In that case, try the needle trick. If that doesn't fix it, chances are it's a big air leak, sticking slide or too rich. :yes: Good luck mate

[Ultrasonic2]

Oh by the way the 4,000 thing only happens at low throttle postions and making the bike richer or leaner via pilot screws doesn't seem to have made much difference to the "Chugging"

[ducatilover]

Oh by the way the 4,000 thing only happens at low throttle postions and making the bike richer or leaner via pilot screws doesn't seem to have made much difference to the "Chugging"

Has it still got the airbox on it?

[Ultrasonic2]

Yes why ?.............

[ducatilover]

Yes why ?.............

Because if it had been removed then you have more problems.

Start as MSTRS said with the Needle height.

[Ultrasonic2]

Yip will do.

Thanks EVERYONE

[MSTRS]

Oh by the way the 4,000 thing only happens at low throttle postions and making the bike richer or leaner via pilot screws doesn't seem to have made much difference to the "Chugging"

They won't. Because once the throttle is opened, that fuelling circuit is more or less redundant.
I don't know about using a washer on those needles. You may just have to go with bigger jets.
What brand and gauge are they? You can't just go up 2.5 or 5 or 10 or whatever. It is really important to use the same brand.
Each manufacturer has different 'sizes'. This is because some are a measurement across the holes, and some are a measurement of flow through the hole.

[Ultrasonic2]

i just tried the washers and that fucked it

can't rev past 4,000 and at 6,000 it dyes i did turn the pilot screws up to 3 though

[bogan]

http://www.dansmc.com/carb_jet_usage1.jpg

theres a pic showing at what throttle opening uses which parts of the carb. Now I assume you have CV carbs? the rubber baffle bit at the top that raises the slide depending on throttle position and rpm. If the rubber baffle bit (i fogret what its sposed to be called) has a hole in it, it would expalin all this, so check them, if not, you can probably assume throttle position=slide hieght.

Now looking at that figure you can see why you have to start at the top and work your way down, most power with the main jet, then the needle for less throttle/power, which slides into the main jet so you tune that after you select the main, and so forth down to the pilot screw which is the last thing you change.

My advice would be do a plug chop (poor mans gas analyser) to check how it is running at the top end, which will tell you whether you have to change the mains. You may be able to get away with only doing it on one cylinder if you're sure they are all jetted the same (and middle ones don't run hotter or something like the rear on vts).

A good explanation of a plug chop is http://hondachopper.yuku.com/topic/20355

[MSTRS]

All the ZXR250 sites show CV carbs.
Now - these can be a bugger to get right/balanced, which is maybe why they aren't still used?
Problem is, you can't check for synchronised slide movement unless the engine is going. And they don't like no airbox. Which means you can't see the little buggers...
They work by vacuum/draft. As you turn the throttle the butterflies on the engine side open, which creates negative pressure in the throat. This negative pressure then acts on the diaphragms, which lift the slides/needles.
Do these carbs have an emulsion tube? It's a sort of sleeve inside the main jet. If so, they could be worn out of round. And if so, the needles are probably also worn. That would explain a heap of your problems.

[ducatilover]

If my memory serves me correct they don't have emulsion tubes.

How big were the washers you used?
Have the carbs been correctly synchronized/balanced and are you 100% sure, willing to put beer on it, that you have no airleaks? Even if the airbox is sitting wrong you will have problems.
I had similar problems on a vt250 spada due to a crack in the airbox, screwing up the operation of the stuuuuuupid CV carbs.

God I love having flat sides now!

[Ultrasonic2]

washers were for 3mm bolts and they were the perfect .5mm

To be honest i wasn't expecting the washers to fix the 4,000 thing cos well i've adjusted the air fuel ratio via the pilot screws and that didn't change it.

i have fix 2 major air fixes . one being there was only 1 of the 4 bolts holding the slide cover on.

Im tending to agree that it's likely to be a balance issue not a fueling one. Still i think it needs a rejet.

This place looks good for jets for my carbs

http://www.pjmotorsports.com/keihin-jets.html

[bogan]

washers were for 3mm bolts and they were the perfect .5mm

To be honest i wasn't expecting the washers to fix the 4,000 thing cos well i've adjusted the air fuel ratio via the pilot screws and that didn't change it.

i have fix 2 major air fixes . one being there was only 1 of the 4 bolts holding the slide cover on.

Im tending to agree that it's likely to be a balance issue not a fueling one. Still i think it needs a rejet.

This place looks good for jets for my carbs

http://www.pjmotorsports.com/keihin-jets.html

Repeat it with me, the pilot screws only change the very low end air/fuel mix it does not adjust the air/fuel ratio across the whole range!

do the plug chop, there's not a lot of point adjust bits willy nilly, especially if you want the carbs to stay balanced (there 2 or four of them?). Getting an idea of what is happening at the moment will enable you to choose the right jets to put in. Though I'm assuming you have checked the current ones for wear and that they don't just need replacing?

[Ultrasonic2]

Repeat it with me, the pilot screws only change the very low end air/fuel mix it does not adjust the air/fuel ratio across the whole range!

do the plug chop, there's not a lot of point adjust bits willy nilly, especially if you want the carbs to stay balanced (there 2 or four of them?). Getting an idea of what is happening at the moment will enable you to choose the right jets to put in. Though I'm assuming you have checked the current ones for wear and that they don't just need replacing?


dood you know less about carbs than i do

your posting links to carbs that dont have SLIDES in them

Heres a link about slide carb fueling
http://hondanighthawks.net/carb14.htm

http://hondanighthawks.net/carb14_files/image007.gif

and like in the pic the pilot screw DOES affect feuling across the whole rang. Since i've been playing with it i know for sure it does too.


Also the spark plug thing is right and i've done that on cars but it's completly impractical to do on a ZXR. to get the spark plugs out you have to take 1/2 the bike apart and thats not practical on the side of the road.

[bogan]

dood you know less about carbs than i do

your posting links to carbs that dont have SLIDES in them

Heres a link about slide carb fueling
http://hondanighthawks.net/carb14.htm

http://hondanighthawks.net/carb14_files/image007.gif

and like in the pic the pilot screw DOES affect feuling across the whole rang. Since i've been playing with it i know for sure it does too.


Also the spark plug thing is right and i've done that on cars but it's completly impractical to do on a ZXR. to get the spark plugs out you have to take 1/2 the bike apart and thats not practical on the side of the road.

ahh yes, the slideless carb, the holy grail of motorcycle fueling technology :facepalm:

If you read the article it also says

Both the pilot air screw and pilot jet affects carburetion from idle to around 1/4 throttle

But fuck it, you obviously know how to keep a bike in tune right? :bleh:

[MSTRS]

dood you know less about carbs than i do

\

With that attitude, don't be surprised if all the friendly, helpful, knowledgeable people, whose brains you want to pick, tell you to go fuck yourself...

[Taz]

Well ya get what you pay for :lol:

[Katman]

Still i think it needs a rejet.



Based on what - your extensive knowledge of all things mechanical?

:facepalm:

[Ultrasonic2]

Any one else want to have a go ? for no apparent reason ?

I dont know what you lot are making such a big deal over Bogan man ways the one posting unrelated info NOT ME.
Im not to worried about it we've all been there before posting before reading the previous posts or missunderstanding them

But feel free to join the band waggon anyway, Not that it helps anyone in any shape or form.

Oh well

[Katman]

Any one else want to have a go ? for no apparent reason ?



Don't take it to heart but you clearly don't know shit from clay.

[Ultrasonic2]

Don't take it to heart but you clearly don't know shit from clay.

i dont take it personally

and yet again i'll point out that Bogan was wrong and i was right so Although i agree i don't know all shit. i do know some shit.

Now i realise that this pointless name calling may never stop so i wont reply to anymore of this sillyness . Obviouly if it's topic related i will though

Thanks guys for your suggestions so far and your friendly banter :-)

[bogan]

i dont take it personally

and yet again i'll point out that Bogan was wrong and i was right so Although i agree i don't know all shit. i do know some shit.


Sometimes when you explain things to people who are learning, you simplify things a bit, yes the pilot screw may change the top end/mid range mix slighty, but it is not what you use to adjust it properly! Some would actually consider that helpful advice.

I'm sure theres a witty analogy comparing that with some other adjustment, but I think I'm already being generous enough in that I haven't told you to go fuck yourself with a plug spanner.

[Ultrasonic2]

, yes the pilot screw may change the top end/mid range mix slighty, but it is not what you use to adjust it properly!
.

i agree that adjusting the pilot screw is the INCORRECT way to richen the bike which why i started this thread about changing the JETs.

[sinfull]

My bike's running rough too but i dont think it's the jetting

226604

[Drew]

I kinda haven't seen anything so far that shows the carbs are the right place to be looking for the problem. At 4000rpm the bike runs rough on a low to medium throttle yeah? So it runs fine with the throttle WFO (wide fuckin open)? If it's fueling causing the problem, I'm willing to bet it's getting air that it shouldn't be.

Only time I ever managed to correct an issue such as this however (after ruling out an air leak), was to do the valve clearances. Most of the older bikes stop getting proper services these days, and this is a rather big one to stop doing.

[MSTRS]

My bike's running rough too but i dont think it's the jetting



Rolls Royce aero engine, is it? Even though your post has little bearing on this thread, I'm sure there's a jet involved in there somewhere...

[schrodingers cat]

Why not take it to someone who knows this shit. Ask them to explain what they did and why.


That way you'll learn something without all the grief.
They may also diagnose an entirly different issue.


A wise man learns from others mistakes.
It may be that YOUR purpose in life is to serve as a learning experience for others

[Ultrasonic2]

ok well im gonna buy my self a set of quad carb sync's

and probably some 128 and 130 jets this will enable me to step up once or twice with the 122 and 125's it has now ..

I really want to buy a 90 degree screw driver too so i dont have to take the RAD off to sync them and also i could screw with the pilot screws while the carbs are still on which would be nice.

Pitty i dont have the cash for anything. Xmas next week

[Drew]

ok well im gonna buy my self a set of quad carb sync's

and probably some 128 and 130 jets this will enable me to step up once or twice with the 122 and 125's it has now ..

I really want to buy a 90 degree screw driver too so i dont have to take the RAD off to sync them and also i could screw with the pilot screws while the carbs are still on which would be nice.

Pitty i dont have the cash for anything. Xmas next week

Let me join everyone else on here in telling you the pilot screws make no difference to anything once the throttle is open. They pretty much never need altered other than for massive climate changes or swapping to avgas/methonol.

If you try and fuel it to run smooth at 4000rpm you are likely gonna cock things up elsewhere in the rev range.

Here is a real easy way to look for air leaks by the way. Get yourself a can of engine start spray. Fire the bike up like normal and hold it around mid revs. Then spray the engine start around the carbs and air box, but not at the proper air intake. When the revs jump you know where to look.

Do this when the engine is not overly hot, and dont have a smoke in your mouth at the time. If you have an account at BOC or the likes do it with an inert gas as it's safer.

[ducatilover]

Any luck yet? :yes:

[The Pastor]

I could be wrong, but most m/c needles I've seen have 5 grooves with a circlip in one of them to set the needle height. Circlip is commonly in groove 3 x factory. Mostly, the needle just drops through a hole in the slide, the circlip dictating how far. Different carbs have different ways of holding the needle down, once it's in the slide.

yeah you are wrong. there are lots of different needles out there, adjustable and not.

[The Pastor]

ok well im gonna buy my self a set of quad carb sync's

and probably some 128 and 130 jets this will enable me to step up once or twice with the 122 and 125's it has now ..

I really want to buy a 90 degree screw driver too so i dont have to take the RAD off to sync them and also i could screw with the pilot screws while the carbs are still on which would be nice.

Pitty i dont have the cash for anything. Xmas next week


I would suggest that the cheap sync gauges are not very good. I've used a lot of differnt methods, and after getting them "spot on" with the cheap gauges it still ran like shit. Called up george from motorcycle doctors and he came out with his yamaha brand ($700) single gauge and balanced them - and man what a difference it made!

I think the cheap gauges work well for the lower end of the performance bikes, but the zxr and cbr's really benefit from a great balance.

I havn't read much in here as to why you're doing it, but due to the time and cost involved i'd be looking at a free flowing intake and exhaust before you jet the carbs to suit. Jetting with out a dyno takes a lot of time, and adjustment - it took me the best part of a year to get my cbr jetted to how i wanted it.... my cbr is now running 145 jets all through out. I want to change the pilot jets out too.... maybe :P

oh and then there is the cams that i want to play with :D

[kiwi cowboy]

I would suggest that the cheap sync gauges are not very good. I've used a lot of differnt methods, and after getting them "spot on" with the cheap gauges it still ran like shit. Called up george from motorcycle doctors and he came out with his yamaha brand ($700) single gauge and balanced them - and man what a difference it made!

I think the cheap gauges work well for the lower end of the performance bikes, but the zxr and cbr's really benefit from a great balance.

I havn't read much in here as to why you're doing it, but due to the time and cost involved i'd be looking at a free flowing intake and exhaust before you jet the carbs to suit. Jetting with out a dyno takes a lot of time, and adjustment - it took me the best part of a year to get my cbr jetted to how i wanted it.... my cbr is now running 145 jets all through out. I want to change the pilot jets out too.... maybe :P

oh and then there is the cams that i want to play with :D

I took my gsxr400 to as bike shop to balance the carbs and when the set said they were balanced the bike ran like crap so made my own set with clear tube and auto trans fluid worked a treat balanced perfect and goes like a cut cat on the track:yes:

[Ultrasonic2]

i didn't get much done lately cos it's been raining.

I was wondering about the cheap sync gauges i think i'll have to calibrate them to each other before they'd be to use full.

i had a cbr before it went very well in the end i got 50hp on red barons dyno . im sure this bike it's there yet.

What jets were you running before ?

Thanks for the support everyone

[imdying]

Yes you sync them all together off of one cylinder before you start. The cheap ones work fine, you just need to be patient and actually understand what it is you're trying to achieve and how to effect the changes that make that happen.

[ducatilover]

i didn't get much done lately cos it's been raining.

I was wondering about the cheap sync gauges i think i'll have to calibrate them to each other before they'd be to use full.

i had a cbr before it went very well in the end i got 50hp on red barons dyno . im sure this bike it's there yet.

What jets were you running before ?

Thanks for the support everyone
How did you manage 50hp from a CBR assuming it's a 250? :blink: Or was that calculated crank hp? Highest standard CBR i've seen was 36rwhp.

I have used a cheap gauge to sync carbs before, worked well for me.

[sugilite]

Just my 10 cents worth, yes, washers do work. I recommend making only one change at a time to avoid getting lost. Pay attention to Drews posts, they are gold for you in this instance me thinks :yes:

[Ultrasonic2]

im gonna concentrate on ensuring the crabs are sync'd before i do anything more

[ducatilover]

Nothing worse than un-synced crabs......:laugh::killingme: :rofl:

[Max Preload]

The cheap ones are fine for balancing. If you have any doubt, simply swap them around to see if they're still showing as balanced.

But as an actual diagnostic tool, not so much. Liquid gauges are useless for that anyway, hence I have dial type.

[Katman]

It pays to ensure that your valve clearances are all good before balancing the carbs.

[Ultrasonic2]

carb balancer and 90 degree screw driver is in the mail