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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.