Engine response at low revs.

[Ultrasonic2]

The pilot screw sets the mixture at low revs/idle. Once the throttle is twisted more, the needles clear more of the main jets to increase fueling. You do know that you have 4 carbs? The problem may be in any or all of them.
Sometimes the symptoms you describe can be caused by a coil breaking down under load, esp once warm.
Or even just worn plugs.

yes i know there are four carbs i've already had them apart .

It really doesn't feel like and ignition issue as i've had that kind of problem before and it feels very different. but is could be an ignition issue all the same.

UPDATE

interstingly the screws were set between 3 and 3-1/4 turns already. i set them to 3.5 anyway. i really want to try them at the stock 2.5 now. arr it never ends

[Ultrasonic2]

Well fuelling seems better now . that could because of

Replacing the missing slid cover bolts
Increasing the turns on the pilot screws
Changing to 91 from bp 98

The chugging is still there, however im wondering if that issue has nothing to do with the fuelling but to do with the heavily worn chain. ( which will be replaced soon )

[MSTRS:Me]

Why would a badly worn chain made the engine 'chug'? Smooth rolling and gear changing, yes, but not how the actual motor runs.
No - if the engine is chugging/not running smoothly, then you have one or more cylinders not working to full capacity. That can be fuel, compression or electrics...nothing else.

[Ultrasonic2]

right after a few days of comuting and well i think really nothing has changed :-(

I took her apart again and changed the pilot screws back to the stock 2.5 turns and well the choke is much less sensatice now which is good but it likes to idle at 3,000 rpm for a while before settling down. i went for a long ride ( not a commute ) and well putting the screws back to 2.5 has REALLY reduced the bottom end power . Chugging hasn't really been effected. But i need to do some comuting before i call anything. At this stage im gonna turn the screws back up . It does make me wounder if it's running lean up high too .. need a dyno and a lamda for that i guess.

[MSTRS:Me]

... it likes to idle at 3,000 rpm for a while before settling down. ...

That is a sign of either an air leak on the engine side of the carbs ...
OR one or more of the slides is hanging ...
OR one or more of the needles is not seating well...

[Ultrasonic2]

Yeah man at 2.5 turns the bike really sux. will put back to 3.5 soon

oh and the idle at 3,000 only happend since i changed the turns

[MSTRS:Me]

How many turns out does the manual say?
See - if 2.5 is right, then you have an air leak. By increasing to 3.5 turns, you are adding fuel. Which somewhat offsets the extra air.

[Ultrasonic2]

How many turns out does the manual say?
See - if 2.5 is right, then you have an air leak. By increasing to 3.5 turns, you are adding fuel. Which somewhat offsets the extra air.

Manual says 2.5 but the bike is not stock

i pretty much proved Trademe900's comments below to be connect


Another suggestion whilst you are working on the carbs is to adjust the pilot jet screws, it really makes a difference. My bike had an unsteady idle and hanged after blipping throttle, slowly returning down. I suspect a lot of ZXR's are like this... running lean on the pilot circuits. I just used trial and error taking off the carbs, adjusting them, refitting and eventually went from to 2.5 turns out (factory setting) to 3.5 (richer) and its got a nice pulsing idle and the revs drop nicely now!

[MSTRS:Me]

I will guarantee they didn't come from the factory like that. In what way is your's not stock?

[Ultrasonic2]

Different headers and muffler and air cleaner

O i have discovered that the chuging only happens around 4,000 rpm .

[MSTRS:Me]

OK. So you have increased breathing...ie more flow in and out. That necessitates increasing fueling so it doesn't run lean. Adding an extra turn to the pilot screws would sort it for idling. But what about the main jets? Or the needle settings?
Perhaps you could try lifting each needle by one groove? See what happens to that flat spot.