ZXR250 - hesitation and stalls when warm

[Grasshopperus]

Hi there,
I've got a 1990 Kawasaki ZXR250, 4-cylinder, 4-stroke and it's got a problem.

The bike starts quickly and happily when it's cold. I put the choke on for a little while and after a minute i turn it off. I then jump on the bike and head out for a ride. After a while (at least 20 minutes) the bike will sometimes stall when I stop giving it gas ie. come to an intersection or set of lights. When it stalls the revs slowly decrease from around 1500rpm to zero, I can see it happening and have become adept at keeping up the revs as I slow down.

After it stalls it becomes very difficult to start again. The battery is new and it tries pretty hard to start again but i usually have to wait up to a minute for it to catch.

I also have a problem with throttle hesitation. When I open the throttle up quickly (not just close then full open, also from say 30% throttle) it bogs down until it gets to around 10K revs and then pulls alright until red-line of 19K. I don't usually give it that many revs so that is just FYI.

I've seen there are people posting similar threads at the moment but this situation is a little different. I'm not sure if the differences are important or not. I'm not a mechanic so pretty unsure.

The weird thing is that it starts fine when cold and idles happily. When I get home after a decent ride (where I've had it stall) it'll happily sit in my garage idling as if nothing happened.

Can anyone help?

[gwigs]

Could be many things,check out this site..http://www.dansmc.com/mc_repaircourse.htm
number 10 .trouble shooting

[Grasshopperus]

Could be many things,check out this site..http://www.dansmc.com/mc_repaircourse.htm
number 10 .trouble shooting

Thanks mate, that site is awesome!

[wrenchjockey]

hi,you dont say if the bogging down is worse when hot.my guess is it will be.how many miles has it done?i would think that there is wear on the needles and needle jets making the bike run rich in the mid range.you may be able to lower the slide needles if!! they are adjustable.also make sure the float heights are correct.not to high.before you start changing carb settings i would check valve clearances.could also cause this problem(if they are tight)i have been repairing bikes for over 35 years and the high preformance 250 4"s can be very tricky to get right as they get older. regards barry

[Harris Ang]

Just had the same problem today.. But I didn't let the bike warm up before riding.. Hopefully it'll go away after 2-3 mins of warming up.. crossfingers.. if not.. Service!

[tigertim20]

sounds similarto myold FZR.the diagnosis was carbon buildup around the valves, which eventually got t othe point where the valves couldnt seal properly and she wouldnt go at all

[Rhys]

Have you tried giving it a hard ride lots of full throttle with plenty of revs! They can start to run a little ruff if not ridden hard, or if its had lots of town or low speed riding.
Bit like a lot of 2 strokes

[racefactory]

Hi there,
I've got a 1990 Kawasaki ZXR250, 4-cylinder, 4-stroke and it's got a problem.

The bike starts quickly and happily when it's cold. I put the choke on for a little while and after a minute i turn it off. I then jump on the bike and head out for a ride. After a while (at least 20 minutes) the bike will sometimes stall when I stop giving it gas ie. come to an intersection or set of lights. When it stalls the revs slowly decrease from around 1500rpm to zero, I can see it happening and have become adept at keeping up the revs as I slow down.

After it stalls it becomes very difficult to start again. The battery is new and it tries pretty hard to start again but i usually have to wait up to a minute for it to catch.

I also have a problem with throttle hesitation. When I open the throttle up quickly (not just close then full open, also from say 30% throttle) it bogs down until it gets to around 10K revs and then pulls alright until red-line of 19K. I don't usually give it that many revs so that is just FYI.

I've seen there are people posting similar threads at the moment but this situation is a little different. I'm not sure if the differences are important or not. I'm not a mechanic so pretty unsure.

The weird thing is that it starts fine when cold and idles happily. When I get home after a decent ride (where I've had it stall) it'll happily sit in my garage idling as if nothing happened.

Can anyone help?

Everything you describe fits the description of a rich condition. If it starts up straight away when cold especially without choke then it is running rich on the low speed circuit/pilot jet/idle jet.

If it pulls nicely up top then the main jetting is good. Set your pilot screws to factory settings in the manual. Your needles could be worn, letting excess fuel through to cause a rich condition that would explain your slow revving to 10k. Try putting the clips up one notch on the needles and see if it makes it better.

[ducatilover]

Everything you describe fits the description of a rich condition. If it starts up straight away when cold especially without choke then it is running rich on the low speed circuit/pilot jet/idle jet.

If it pulls nicely up top then the main jetting is good. Set your pilot screws to factory settings in the manual. Your needles could be worn, letting excess fuel through to cause a rich condition that would explain your slow revving to 10k. Try putting the clips up one notch on the needles and see if it makes it better.

Racefactory beat me to it.


Check your airfilter too, if in doubt, replace it, they're cheap and your bike will love you.
I'd gamble your needles are in need of replacing though.
But, a lot of those smaller bikes won't pull cleanly at full throttle below 10,000. Roll the throttle on and see what happens.

[Harris Ang]

So yea, bike WAS running rich probably because I was using 98 instead of 91 so far haven't had an engine stall..

"Rhys

Have you tried giving it a hard ride lots of full throttle with plenty of revs! They can start to run a little ruff if not ridden hard, or if its had lots of town or low speed riding.
Bit like a lot of 2 strokes "

If i were to nanny ride it all the time ie not thrash it.. 10k+ revs will it do more damage than good? Or is it good to thrash it once in a while?

[tigertim20]

So yea, bike WAS running rich probably because I was using 98 instead of 91 so far haven't had an engine stall..

"Rhys

Have you tried giving it a hard ride lots of full throttle with plenty of revs! They can start to run a little ruff if not ridden hard, or if its had lots of town or low speed riding.
Bit like a lot of 2 strokes "

If i were to nanny ride it all the time ie not thrash it.. 10k+ revs will it do more damage than good? Or is it good to thrash it once in a while?

theyre built with an 18k redline or so. high rpm isnt going to hurt it, jesus they do near 10k just sitting at the open road speed limit. nothing wrong with revving it man, its a sportsbike, thats what it was built for

[racefactory]

theyre built with an 18k redline or so. high rpm isnt going to hurt it, jesus they do near 10k just sitting at the open road speed limit. nothing wrong with revving it man, its a sportsbike, thats what it was built for

Yup what he says. These bikes have proven to last forever at 20k rpm on the race track.

[Ultrasonic2]

WOOOO HOOOO

some else with the same bike and the same problems . i also took it to a place and they didn't know what was wrong with it too.

I also have EXACTLY THE SAME ISSUES AS YOU. TO THE LETTER !!

Now i also went down a track for AGES thinking the bike was Rich but that was TOTALLY WRONG

The bike is WAY to lean

i presume this bike isn't stock any more and it's now way to lean

With the pilot screws at the 2.5 turns out my bike at the lights will idle lower and lower until it stops. The bike is to lean you need to increase the turns to 2 3/4 to 3 turns. this will allow your bike to idle again. you will also notice the bike is much faster.


Now when you jam open the throttle and it dies alot of people will say it's rich. in this case they are wrong. again the bike is miles to lean and you need to start increase the main jets on the bike like i have.

The cool thing is i know your bike must be slow as and once you increase the fuel the thing will fly like you couldn't imagine.

[ducatilover]

Pilot screws will not make your bike faster, they have nothing to do with it's high RPM running, they are redundant after 3000rpm.
If it is that lean, it will be very flat in power, rich will make it surge, it will also back fire off the throttle when it's to lean.
If it has problems idling and it hesitates when hot, it's too rich.
If you rev it when warm and it drops below normal idle and climbs back up again, it's too rich.
If the revs drop slowly it's too lean, or there are sticking slides/throttles.

[Ultrasonic2]

Pilot screws will not make your bike faster, they have nothing to do with it's high RPM running, they are redundant after 3000rpm.
this is a common kiwi biker comment and i can understand why it's seemingly become law here. Obviously carbs are different so it's hard to make a blanket statement about them if the carb in question wasn't a slide carb i would tend to agree with this comment in general. With slide carbs it's a bit harder. If you search on slide crabs you'll find some people suggesting that the screw we're adjusting will affect the whole range.

At the end of the day the It's relatively easy to tell, when you dis mantel the carbs you can follow the gernals and it's pretty easy that on THIS carb it's impossible for the fuel to stop flowing through these channels.

And at the end of the day if he adjusts the screw he will crease his performance across the whole range. i know i've spent ages playing with this screw



If it is that lean, it will be very flat in power, rich will make it surge, it will also back fire off the throttle when it's to lean.
Totally agree and his power is flat but he doens't know it because he hasn't got anything to compare it against.

His bike will be heating up real fast to, too 1/2 way (where the fan comes on) but there again he does't have anything to compare against so doesn't know any better



If you rev it when warm and it drops below normal idle and climbs back up again, it's too rich.
If the revs drop slowly it's too lean, or there are sticking slides/throttles.

At the time i had my idle at 2.100 rpm and it slowing gets slower and slower and stops. increasing the fuel via the pilot screw fixes this

I have spent a year on this issue with my bike and i know his will be the same.

if we take a look at the issue in it's most basic form the bike wont be stock allowing more air into the engine. So with stock fuelling the bike will be lean, so he needs to add more fueling to correct the air/fuel ratio


peace out :-)