Revs by itself when warm.

[Equalz]

Hello guys, I have been meaning to register here for a long-time and I finally have!

Okay let me begin, I have a beautiful Kawasaki ZXR 400 L1, after it has been started up and idled or ridden for 5 minutes or so when you open the throttle and rev it a bit it doesn't crisply go back to the idle.. It hovers at about 2k revs for a few seconds then drops back to the 1200rpm idle. So far I've dis-assembled the throttle body on the bars give everything a good clean (was a bit crapped up), tested again but to no avail! Did the same where the throttle cables attaches to the carbs and again unfortunately with no result!

So I figured that perhaps it was due to an air-leak. Tried spraying some carb cleaner in-between the airbox and the carbs when it's stuck at the 2k RPM a few times and it had no effect, did the same between the carbs and then engine and again it had no effect so I'm beginning to think it's not an air-leak.

Is it possible that my pistons are worn? I know I'm assuming the worst case scenario but I can't think of anything else. I also tried putting my hand over the air intake with the tank off and it didn't solve the 2k RPM stick which also makes me think it isn't an air-leak once more..

May I also add that there is no blue smoke from the exhaust which then makes me think that maybe the pistons aren't worn.. I'm really scratching my head here!

[guitarcarrot]

Welcome to the forum! And congratulations on seemingly knowing how to use the search function I actually have exactly the same problem, I have pretty much started to ignore it now, is it restricted by any chance? I doubt worn pistons, try balancing the carbs very well, that helped me out a lot, but made it bearable, hoiw many miles on the bike?

[Equalz]

Thanks for your reply, 9265 miles on the bike and it's full power with a full micron system & K&N, stripped and cleaned the carbs down just a couple of weeks ago too ..

Oh forgot to mention. if I push the throttle forward when it's sticking at 2k it goes back to idle. I know that would make you think that the throttle is sticking but it definitely is not

[RedexRobB]

An air leak was my first thought but that seems not to be the case.

You say the revs drop when you push the throtte closed, although you may have cleaned up the throttle up at the bars there a load of working parts on the carbs too. Have you run oil down the cables as these could well be sticking? As well as that I would get the tank and air box off and make sure that the throttle is closing properly. If you open the throttle and (engine doesnt need to be running for this) let it close on its own, where the cables are fitted to the carbs the rotating part they fit to should shut all the way. You know if it has because it will go all the way to the throttle stop/idle adjuster. If it doesnt then give the springs between all the carbs a clean and stick a couple of drops of oil round the springs and work it till it does what its supposed to. You may want wind the throttle stop/idle adjuster most of the way back, that way you get the ful travel of the throttle and will work the oil in a bit more. Just have a fair idea of where it is before you wind it back, that way you wont be guessing where it was.

[dan]

The wife's bike does this - her's is a slightly warped air box which occurred year's ago when it was dynoed and now it doesn't seal properly.

I know it isn't the cables as they've been replaced, and the carbs stripped and cleaned, and new plugs.

I just live with it when I ride tbh

[R P Corse]

My bike does this, the bell mouths are slightly knackered in the airbox on mine, but then my bike idles around the 1500rpm mark and maybe a touch higher! that said, it also stops if I hold the front brake and slip the clutch a little.

[dan]

My bike does this, the bell mouths are slightly knackered in the airbox on mine, but then my bike idles around the 1500rpm mark and maybe a touch higher! that said, it also stops if I hold the front brake and slip the clutch a little.

Is exactly what I do!

[R P Corse]

No idea what it is, it could be an air leak, wouldn't surprise me if it is on mine as it an H1! Lol but haven't had the time to really give it the once over to confirm it.

[Tirpitz]

Tight valves will also cause an uneven idle.