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Discussion Starter #1
I have a 2004 ZX10R and after the engine is warmed, past 160 degrees F, the idle will slightly raise then almost stall, then raise and almost stall again. If left idling too long without revving the engine, the engine will die. Lately, especially in hot weather, the engine will get jerky and surge while cruising at slight throttle. If revved it will clear up and it always accelerates without issue. This will never happen if it is a cool day and the temp never raises over 160 degrees. In fact, it runs great and cruises great just as long it is kept under 160 degrees. I have checked all the vacuum lines and nothing seems to be out of place. Any ideas what is going on?
 

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First thing I think of is a air leak.

TB boots cracked/sealing good?

When was last valve adjustment done?

When was last time TB where balanced?

When was last time bike didn't have this issue?

Have you done anything to it lately?
 

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Discussion Starter #3
I checked the valves about 3000 miles ago and they were still in their limits.
I have to say,,,the issue did start shortly after that, but i looked over everything again and nothing appeared out of place, torn or damaged.
And, why does it only occur after the engine temp goes above 160 degrees. It's weird to see it warm up and idle perfect until that temp goes above that mark, then it starts to vary.
 

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"Best guess"

If there's a air leak.

When the engine is cool, the enrichment circuit
would kick in adding fuel.

As the engine warms up the enrichment circuit starts cutting back and
creates a lean condition.

I'm guessing you removed throttle bodies when you checked the valves
and started shortly after that.

Still sounds like air leak at the TB boots. Maybe you have the TB
half cocked or boot(s) cracked not sealed well. Wouldn't be the first
time I've seen bad sealing boots on a bike that's 14 years old.

test - warm the bike up and when it starts doing it's funky thing
spray some WD40, propane, starter fluid, etc. around the TB boots
and see if anything changes.

If there's a air leak it will get sucked in and revs will change. No leak, then
no change in revs.

Sure wouldn't hurt to balance the TB's either.

That's all I got.
 

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Discussion Starter #5
I owe you big time "BOTTOMS UP". I decided to pull the throttle bodies to look them over and look at the boots underneath. The two inner boots' clamps had become loose and the tightening nuts came off the bolts. I tightened them correctly and snapped everything back together. Smooth idle and ran a lot cooler.
Thanks again.
 
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