Cranky when hot

[BladeBoy]

Any idea's as to why my ZXR gets cranky when it gets hot?
slow going in traffic seems to do it, although the temp gauge does indicates normal temp, at idle to about 3000 RPM it gets the stutters, once underway and cools down a little it is OK, I have checked and the fan is cutting in, have new plugs, filters ect, balanced the carb's and I don't use optimax any more, ?????????
Mark.

[mattyv74]

Are you sure its whenit gets hot? or could it be sitting on really low revs for a period of time causing it to load up?
Just a thought.

[BladeBoy]

I can idle it from cold, will be OK but if I have been riding then idle it stuffs up, I pulled the plugs when this first started and they were OK, replaced them anyway with Iridium types did not fix the problem, heat soak, too rich at the bottom end ????
Mark.

[Smitty]

Any idea's as to why my ZXR gets cranky when it gets hot?
slow going in traffic seems to do it, although the temp gauge does indicates normal temp, at idle to about 3000 RPM it gets the stutters, once underway and cools down a little it is OK, I have checked and the fan is cutting in, have new plugs, filters ect, balanced the carb's and I don't use optimax any more, ?????????
Mark.

hmmm
a contradiction here thats not helping....
how can the fan be cutting in....if the temp gauge is normal??
so
can we have sum more info on the bike pleeze
can? Dynojet kit? how many ks
and its a 750? or the 250? version


cheers

[BladeBoy]

Yoda,

ZXR750 H1, about 50,000Klm, the fan cuts in when it is suppose to, just above normal on gauge, sports can, I don't know what brand, standard jets.

Thanks,
Mark

[Smitty]

Mark
ta mate
your answer suggests fuelling..specially the 0-3000 bit
and I note
you have replaced the plugs and air filter

have the H1 manual at home
will check for sum more suggestions when I get in

cheers

[mike-s]

I'm pondering how your thermostat is handling things, i.e. is it cutting in/out correctly or not *ponders*

[Steve_TLS]

A long shot. Could be a coil being affected by the heat of not moving. I'm pretty sure they run a wasted spark so it's 2 coils and each one does 2 cylinders.

But it will be hard t oconfirm this without a known good spare.

[Aussie Ninja]

I would think that if it was the fuel mixture problem it would happen when cold. If the carbies haven't been touched the filter and pipe should lean the mixture, and with no engine heat the intake air stays dense. Once the bike heats up the air going in loses density effectively making the mixture richer. So any idle circuit mixture problem should manifest when the bike is cold.

I chucked a jet kit in my bike and the suggested idle setting was 3 turns. when cold it idled fine but you could smell the fuel. Once it was heated up the poor thing was drowning in fuel and struggling to idle. Yours sound like that?

I've just contradicted myself in one post. Outstanding.

[BladeBoy]

Yoda, Aussie Ninja,

It does not sound or feel like it is drowning in fuel, rus OK then starts to stumble and the exhaust note "rolls" I know this sounds a bit strange, then it will run OK, I suppose it could be a fueling problem, I am trying a new can tomorrow as the one on it is stuffed,( very loud ) I don't know if too little pressure will make it run shitty or not.
Thanks for your input.
Mark.

[Smitty]

if its not missing and you have replaced the plugs
I reckon its not electrical

assuming you have a good mechanical engine (decent compression etc)
I reckon you are looking at the fuel system
why?
the infernal combustion engine basically needs 3 things to go...
an ignition source, an air/fuel mixture and means of compressing it
1 and 3 you have
has to be #2...


when was the last time you cleaned the bowls out
or ran a fuel system cleaner thru it...?


cheers

[BladeBoy]

Yoda,

I cleaned out the carb bowls about two weeks ago, and put fuel cleaner in at the same time. replaced fuel filter and fuel lines, plugs, air filter, and bought a carb balancer and did that as well.
Question.
I did notice that although I could balance the carb's at idle, but if I raised the revs up to 3000 the balance would be out, not by much about one or two divisions, if I balanced it at 3000 revs it would be out a bit at idle, I am not sure if this is OK or not.
Mark.

[Smitty]

Question.
I did notice that although I could balance the carb's at idle, but if I raised the revs up to 3000 the balance would be out, not by much about one or two divisions, if I balanced it at 3000 revs it would be out a bit at idle, I am not sure if this is OK or not.
Mark.

Mark.....you have sorta answered part of the question....
no its not OK...its the carbs..by your own statement
but why are the carbs going outta balance thru the rev range?
worn something? but I am not sure what
linkage? or a carb thats worn? (or gotta a worn part)
hmmm.....the balancer should indicate if you have one carb thats
not right....
some drawings to think about,......

[Smitty]

Mark
I have been thinking
(thats dangerous, I know)

when you balanced the carbs
noticed any fuel leaks?
and
did you balance/check the fuel bowl levels???
that last point is very important
one carby with a low fuel level
and you can adjust it ALL to idle or rev
but it will stutter terribly in between

in fact, adjusting the fuel levels is something you do before adjustin
or balancing the carbs...

cheers

[Aussie Ninja]

If the carbies are like a 6R the centre two supply vacumme to the exhaust fresh air system. Mabye something is up there. Try diconnecting it and checking the vacumme levels again.