99 XP Limited Uncontrolable high revs!!!

[tech_josh]

Fired up my 99 XP limited for the first time after replacing all of the lines, and it fired right up. Only problem is goes straight to max rpm and never comes down! I pulled off the DESS and it just keeps on revving. Only way to stop it was yanking the plug wires.

The butter flys inside the carbs are not stuck and open, and close with the throttle lever. Im stumped as to why it would stay on with the DESS pulled and keep revving to max rpm with the throttle closed.

Need some help guys.

 

[LouDoo]

You've got an air leak some where, check the base of the carburetors first. If you get a runaway condition again, pull the choke.

Lou

 

[ashr8]

I've been having the same problem myself, I have changed all the lines and had the carbs stripped down, de chocked and up jeted, when reinstalling the carbs I made sure I replaced the gaskets and checked all the lines are tight. When starting it up it was fine for the duration I had it running then I started it up again and it shot off to full rpm any ideas what could be the problem or is there a common place for air leaks on the 951??
Cherers


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[ashr8]

Any ideas fellas??


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[Spimothy Leary]

pull the choke or jam the throttle to stop a run away.

check for exhaust leaks, and turn down the idle from 3000 to maybe 2700ish....

 

[mikidymac]

Your symptoms are as others have said an air leak and if not fixed will destroy the engine. When you have too much air and not enough fuel the combustion chamber gets so hot it does not need a spark and runs like a diesel engine so pushing the stop button and pulling the plug wires will not stop it. They either keep running a t max rpm until the blow or you have to pull the choke or flood them with fuel. I would not start it again until you find the source of the problem. A typical place for them to leek is the thin o-ring on the rotary valve cover. The only way to be sure is to do a leak down test with block-off covers and a low pressure air gauge.

 

[ashr8]

Ok thanks I'll get checking, one thing by rotary valve you mean reed valve because a 951 doesn't have a rotary valve?


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[mikidymac]

Sorry about that, yes reed valve. More times than not I have found that a run away air leak is somewhere in the intake but crank seals can cause them too.

 

[Bnelson]

Would also turn the idle down and see if that helps... I believe the 951's are notorious for running away when the idle is too high

 

[ashr8]

Cheers guys I shall have another go at it.


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[dannyual767]

My lean runaway was caused by an airleak at the base gasket of one of the carbs ('96 XP.) It was my fault, though. I had forgot to tighten up the two bolts. They were barely finger tight :facepalm: . Tightened them up and all was well again.