I want to change the jets in my bike?

**Ultrasonic2** · 17th December 2010, 10:53

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:Me** · 17th December 2010, 12:08

Try lifting the needles first.

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** · 17th December 2010, 12:53

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** · 17th December 2010, 13:13

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** · 17th December 2010, 13:41

Originally Posted by Ultrasonic2

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:Me** · 17th December 2010, 15:33

Originally Posted by 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?

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** · 17th December 2010, 15:47

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:Me** · 17th December 2010, 15:51

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

**ducatilover** · 17th December 2010, 16:05

Originally Posted by MSTRS

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** · 17th December 2010, 16:07

Originally Posted by ducatilover

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** · 17th December 2010, 16:59

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:Me** · 17th December 2010, 17:01

Originally Posted by ducatilover

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

Oh - sorry - I'm following on in this thread from discussion/s here

**bogan** · 17th December 2010, 17:06

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.