EX500 loses power on the track

[Honclfibr]

Been having some issues with the race bike since the june race weekend, thought I had found the issue but it turned out to be a red herring, so I'm picking everyone's brain lately for possible causes...

The bike idles and revs freely and runs strong for about 2-3 laps,
then it starts to bog when accelerating from below 7k or so. If I
keep on the throttle acceleration smooths out around 9k, this
continues to worsen until by the next lap I've got no power at all
and must slip the clutch to keep the bike moving (I can usually drag
it around to pit-in doing this). Once I pit in if I pull the clutch
in the bike idles about 1k below normal (have the idle set to 2k,
idles around 1k). If I turn the bike off and let it sit, it returns
to normal idle in a few minutes and I can get another smooth lap or
two around the track before the loss of power returns.

The problem only occurs on the track, I rode the bike around the pits
during a trackday for ~20 minutes and couldn't reproduce the problem,
let the bike idle in neutral for ~20 minutes and it still revved
freely, the power loss seems to occur only when the bike is being
wrung out on the track.

I've been trying to track down the problem, at first I thought it was
vapor lock (since the problems started occuring during the june track
day, in the heat) and checked the tank vent (unclogged), pulled the
carb vent hose (no change), and replaced the aftermarket clear fuel
line with the stock fuel line (no change). Checked the air filter
(clean) checked the airbox and carb boots (no cracks or leaks),
pulled the carbs and checked the slides and diaphragms (slides move
freely, diaphragms aren't ripped). Thought it might be a head gasket
but my radiator remains full of coolant and there's no oil in the
coolant or water in the oil. Would a compression test definitively
rule out the head gasket? I know they are often a problem on EXs but
I thought they were always accompanied by coolant issues...

Any suggestions on what to look at next? I'm tempted to try to
replace the coils, the idea being that the heat could be causing some
sort of electrical failure, and it's a fairly simple swap. If the
coils were cutting out that could cause my idle to drop as the
unburned fuel would have the effect of flooding the engine. Bad
float heights could flood the engine too, but should cause the bike
to idle poorly and it idles forever like a dream, so that seems
unlikely. Jetting issues that only occur at high load? Micky raced
the bike last year at a much quicker pace than I run and never had a
problem, and I haven't touched the jetting...

Any ideas are appreciated. Hoping to have a few ideas to try for the
upcoming race weekend, so I can tinker in between practice sessions.

[double agent]

replace bike with new or like new . thank you Ill be here all night.

[ssg]

I have no idea, but:

has you or anyone else done headwork to the machine?
is there any 'race prep' type machine work that is typically done to the ex's before racing? (like decking it or using an extra thick HG, etc.).

[union]

My first thought would be a clog somewhere in the fuel system. I know you said you checked it but its what it sounds like to me. Other then that maybe the plugs are going but Im not sure about that.

[OreoGaborio]

[Karaya One]

Coils would be next on my list for sure.

[SSearchVT]

The compression check would need to be done while the bike was good and hot to rule out the gaskets and hard parts. Preferably as quick as possible after the bike is showing the problem.

You should take a good look at the ignition parts. It could be bad coils, or a stator on its way out, or even as simple as plug wires.

What does the oil look like - is it particularly thin - My thought is that if it isn't the ignition it could be clearance between the rings and cylinder. This is a long shot though. Good luck...

[MsHap]

What is the temp like?

I think I would go with ignition also. Coils but maybe simply the plugs heat range.

What do the plugs look like now?

[Honclfibr]

Originally posted by somestrangeguy
I have no idea, but:

has you or anyone else done headwork to the machine?
is there any 'race prep' type machine work that is typically done to the ex's before racing? (like decking it or using an extra thick HG, etc.).

I'm sure it's had headwork done in the past, the stock head gaskets are notorious for blowing in race scenarios. As it was described to me, if you're high in the revs and downshift enough to overrev the bike, you can be pretty much assured that you just blew the head gasket.

This was told to me by the guy who sold me the bike, so I'm guessing he's done one or two

[Honclfibr]

Originally posted by SSearchVT
The compression check would need to be done while the bike was good and hot to rule out the gaskets and hard parts. Preferably as quick as possible after the bike is showing the problem.

You should take a good look at the ignition parts. It could be bad coils, or a stator on its way out, or even as simple as plug wires.

What does the oil look like - is it particularly thin - My thought is that if it isn't the ignition it could be clearance between the rings and cylinder. This is a long shot though. Good luck...

Hmm, it'd be at least 15 minutes from when the bike started hiccuping until I could get a compression reading. That would probably be too long, huh?

Someone on the NEAR site said something about his ZX7 having similar issues. Turned out to be an ignition rotor pickup that would go bad in the heat. Interesting, as they're both similar age kawis.

[Honclfibr]

Originally posted by MsHap
What is the temp like?

I think I would go with ignition also. Coils but maybe simply the plugs heat range.

What do the plugs look like now?

Bike is running cool as a cucumber. I'll double check the plugs but I'm pretty sure they're the stock NGK plugs, I took them out last race weekend and the electrodes were a nice dark greyish/brown, nothing to indicate any sort of lean/rich/detonation problem. Probably worth taking another peek at them again to see if anything's changed.

[TheIglu]

Originally posted by Honclfibr
Hmm, it'd be at least 15 minutes from when the bike started hiccuping until I could get a compression reading. That would probably be too long, huh?

Someone on the NEAR site said something about his ZX7 having similar issues. Turned out to be an ignition rotor pickup that would go bad in the heat. Interesting, as they're both similar age kawis.

Bingo.

My old CB750F did that quite a few years back in college. I thought for sure coils, fuel or overheating. Turns out it was the spark sensor things. Basically the coils that let the ignition know when to fire. They get hot and stop working. For me it cut out two cylinders so it was easy to diagnose on a 4 cylinder bike. I think the proper name is "pulse sensor" or something of that pursuation. I'm willing to wager two shiney nickles on it.

[Stoneman]

It's overheating. Take 'er from there...

[JeffL]

Dont know if you had it fixed this weekend, but I'm guessing it had something to do with fuel starvation?

[OreoGaborio]

yup, clogged petcock lead to a weak fuel flow... he replaced the tank from the EX500 he bought for a freakin song & a dance & his problems were solved

[Stoneman]

Ahhhhhhhh....'mixture problems', eh?

[Awesome]

so your EX around the track is just like Pete around girls? Powerless?

[OreoGaborio]

his bike fine now... it was just acting like you... pullin the saaaame shit... oooverrr & oooverrr again and generally being an asshole.....

[Awesome]

Hey, there was originality there. It got me a chuckle. And I resemble that asshole remark!

You ever seen those movies where guys are writing books and drinking a glass of wine? Well that's me, accept I'm drinking bottles of wine and writing a technical paper for class tomorrow night. Oh, and i've taken two two breaks so far to have sex......with a girl!

[KB]

Originally posted by hessogood
Hey, there was originality there. It got me a chuckle. And I resemble that asshole remark!

You ever seen those movies where guys are writing books and drinking a glass of wine? Well that's me, accept I'm drinking bottles of wine and writing a technical paper for class tomorrow night. Oh, and i've taken two two breaks so far to have sex......with a girl!

Girls on the internet with a camera don't count.

KB

[highsider]

Originally posted by rmbbikes
Girls on the internet with a camera don't count.

KB

And exactly why not?

[Awesome]

Originally posted by rmbbikes
Girls on the internet with a camera don't count.

KB

Is that what JB tells you?

[bump909]

lots of "oh snap"s in this thread

[KB]

Originally posted by hessogood
Is that what JB tells you?

Damn I got nothing. Nice one.

KB