Revving on its own even after spark leads are pulled off?

[MickR]

Hey guys, so went to start my 951 xp seadoo jetski the other day and found a pretty scary problem. It took a lil to start due to a flat batt but when it did i cycled the revs a few times it revved to peak revs on its own... i pulled the leads off the plugs but it kept revving, so i turned off the fuel and disconnection positive and negative off the batt, still revving, so i started taking a spark plug out.. by this time i think the carbs ran dry so it stopped..

So ive got a 2 stroke that was running fine a month ago but now its peaking on its own with no spark? Accelerator cable has free movement and carbi's seem to b opening an closing properly but is hard to tell without pulling the exhaust apart. Spark plug tips are mocha brown. Do i need a carbi rebuild?

[twinrock]

This is called glow pluging..from what I understand the spark plug is getting soo hot its glowing red hot..enough to continue to burn the fuel even when the lead has been removed, and it will rev at full revs..quite scary especially on a cold engine..A main cause of this is an air leak..in the crank case or manifolds sucking in air drastically leaning out the mixture causing it to rev high and over heating the plug.. a compression test may sorce help

[hybrid]

Yeah twinrock is on the money. Most likely a big air leak somewhere. Check your manifolds.
If you can't see anything obvious, it might be crank seals, but it sounds like a pretty big leak.

[JonW]

Had this happen to me, Twinny is correct, it was an airleak between the carb and the manifold for me. check for splits in your manifolds as well.

If you use a gas torch with the buntane on by the flame off you will hear when it starts to suck the butane, but switch it off as the revs rise as once its gets into its stride youre srewed. With my bike i had to hold the brakes and dump the clutch to get it to stop, fuel disconnected, plug lead(s) and switch off made no difference as you know.

[MickR]

Huge help guys, thats awesome! I was ready to spend big dollars on getting my twin Mikuni Carbs rebuilt. I'll hafta go check that out. Get back to ya's to tell you how i went!

[JonW]

Well dont discount the carbs, if the seal on the top of the unit is bad then that could be the problem... but really its usually the manifold(s).