I want to change the jets in my 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/...es-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. 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:Me]

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:Me]

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