ZZR250 won't idle when hot

Been having some idle issues with the ZZR250 over the last few weeks, and can't seem to get it sorted. Initially had the needles and seats changed, then replacement carbs from the wreckers (with new needles and seats from first attempt).

At first it seemed better, ticking over better on choke and running smoother. However, after a 25k freeway ride is stalls a few seconds after the throttle is released. Idle is set just over 1000rmp, and it just gradually falls off and stalls. Fuel tap has also been cleaned out.

It's got me farked - and help appreciated.

Does it smell of excess fuel? Did you also check the vacuum seals on the fuel tap?

Fuel filter ? Tank venting ok ? Choke not staying on ?
Air filter ?

does this happen in colder weather ? as it is the symptoms of carb icing

other suggestions would be disconnect the crankcase brether from the airbox , when you shut the throttle there is a high vaccum and an increase in crankcase pressure pumping hot oily air into the carbs

see how you go with that

..... However, after a 25k freeway ride is stalls a few seconds after the throttle is released. Idle is set just over 1000rmp, and it just gradually falls off and stalls....

sounds like it may be a problem with the low-speed *circuit* in the carbs?

Check pilot jets - they may need a clean (fuse wire is good for this), and also mixture screws......they may need to be adjusted / richened up a bit.

Mike
could be the timing if its only doing it when warm

I am going to say it has a leaky manifold.
I am sure someone else here knows why they only leak when the motor is hot but I ahve had it happen before as you describe and thats what it was. Just check all you boot clamps are tight first before you going spraying around looking for cracks in the manifold rubbers.

I am going to say it has a leaky manifold.
I am sure someone else here knows why they only leak when the motor is hot but I ahve had it happen before as you describe and thats what it was. Just check all you boot clamps are tight first before you going spraying around looking for cracks in the manifold rubbers.

yep another high possibility

another use for aerostart

ive seen this problem on a zzr250 we had the carbs reconditioned checked everything turned out the engine was low on compresion

I have the same problem

Have to set the isdle at 2500rpm for it not stall...Otherwise it just keeps falling and falling(revs) till it stalls.....At 2500-3000 it isdles pefect....


Carbies balanced,,,will check the mixture screw....

PS in mine i couldnt find any leaks.... dose the same thing when tak is removed....So im little low on ideas as well any help is kindly appreciated...

as mentioned above, a compression test can't hurt. At the very least it'll let you know somewhere else where it isn't having problems.

Mike..

Few things i found.

Make sure the rubber band that goes from the airbox from under the tank is attached to the air box properly (if this doesnt seal it, it will not idle properly)

Run a cleaner through the tank (just some spitfire or something)

Make sure you check for the head (i know, simple) but the radiator cap is under the fairings, just have a quick look

Oh and the breather tube for the tank, comes out from where the seat is, can often get "blocked" or cut off by the seat, make sure it's correctly placed and isnt being shut off.

Make sure the rubber band that goes from the airbox from under the tank is attached to the air box properly (if this doesnt seal it, it will not idle properly)

Im not sure what rubber band you are reffering to?

Sounds like you may have a leaking valve,or clearence too tight.
This is a classic case for an engine that does this when hot.
If clearence too little,when engine warms,clearence dissapears and holds valve open slightly,or maybe just a bad sealing valve.
As mentioned above,comp test i reckon.

Comp test done & ok.

In the end it was a combination of really dirty carbs and a stuffed plug cap. Carbs were soaked over night in carb cleaner and a new cap fitted. It now runs like a dream.

Thanks for you input everybody - much appreciated.