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Discussion Starter · #1 ·
I have a 99 ZR700 that does not return to idle right away after high throttle. I have to momentarily open the choke to settle it down after a hard run. I have adjusted the idle mixture screws with little or no change. I have left them 1 1/2 turns out for now. Anybody know what may be wrong here?

Thanks
 

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After high rpm operation, the pipes are very hot. This 'hot' condition of the pipe increases/improves pipe scavenging by making the cylinder run slightly leaner than richer... Which in turn will cause slightly higher idle rpms until the pipes cool down.

Blipping it with the choke makes the fuel/air ratio rich, and a rich mix will run cooler, which in turn will also pump out cooler exhaust gases... With choking, the pipes cool much faster than waiting, and that's why choke-blipping works.

If it's idling high rpm when you shut it down, the motor spins more revolutions than compared to a slow rpm idle. This causes raw unburned fuel to become vapourized and end up in the pipes.

Then... Next time you start it up, the raw fuel vapours in the pipes can ignite, and you get a healthy bang out of the exuast system!

It is perfectly normal for a carbed engine, because carbs cannot adjust according to sensor inputs as EFI would. Just blip the choke or wait a bit longer for the pipes to cool, the rpms will drop, and minimize the chance of 'the BIG BANG' when you start it up again.

:chug:
 

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Is the sled stock, or modified?
Have the carb's been cleaned lately?
What is your hot idle speed set at?

My '99 ZR700 never experienced the "high idle syndrome" which my current ZR8 has. It's caused by a lean mixture closed throttle position.
My '99 was set to idle at 1500 rpm. You could go lower which may help.
The 700's flatsides don't have air mixture screws on the carbs ( 2001+ flatsides do) so you likely need to open the fuel screws. Try openning them up to 2 1/2 turns out and see if that helps. Then if so, slowly bring them back in until you find the sweet spot.
If openning the fuel screws some makes no difference I'd suggest that your carbs need cleaning. You may have gummed up air passages causing the lean condition.

Good Luck!
 

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Discussion Starter · #4 ·
Thanks for the help. Sled is stock, carbs clean, idles 1500 rpm (hot). I bought this sled 3 yrs ago and it has always had this high idle after throttling with the engine hot. It idles around 2500 rpm for almost a minute before droping down to 1500 rpm. Could this leaning out cause engine damage? Should I be concerened? I have tried adjusting the fuel screws in/ out but does not seem to matter. I replaced jets and needles thinking maybe worn or damaged but no improvement was found.

Thanks again
 

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<div class='quotetop'>QUOTE (psblair911 @ Jan 22 2007, 01:06 PM) <{POST_SNAPBACK}></div>
Thanks for the help. Sled is stock, carbs clean, idles 1500 rpm (hot). I bought this sled 3 yrs ago and it has always had this high idle after throttling with the engine hot. It idles around 2500 rpm for almost a minute before droping down to 1500 rpm. Could this leaning out cause engine damage? Should I be concerened? I have tried adjusting the fuel screws in/ out but does not seem to matter. I replaced jets and needles thinking maybe worn or damaged but no improvement was found.

Thanks again[/b]
No, nothing to worry about. Most of all my sleds have always done that and have never had a problem because of it.
 
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