Just bought an 07 yfz450. Its been running great since i bought it a few weeks ago. Until the other day i was riding the woods and stopped to take a pee. I left my quad running and out of nowhere why i was sting by a tree the quad started reving up higher and higher by itself then it died. Now everytime i turn it on it revs high on its own Nd shuts off. Today i tried to start it and it would t even start. It happened out of nowhere while it was idling.. I checked my jets and they all look clean. I looked for air leaks around the boots and cant find anything. What could it be?!

 

You could also have an air leak around the exhaust manifold or head gasket. How hard were you running it before the idling, and how long did it sit idling when it first started? Is your radiator clogged? Cooling fan working? I ask this because they don't have the cooling reserve to sit and idle for long periods of time. It is possible the head may have warped if it overheated.

 

It was only idling for about 40 seconds before it started reving up. And i wasnt riding too hard. I usually stop about every 5 minutes of riding just to let it cool off so i check my phone.

 

Bump

 

How did you check for air leaks? For whatever reason your air/fuel ratio at idle is to lean. Since it happened while running I would be suspicious of a blown head gasket/warped head. I would also look at the rest of the fuel system. Float heights adjusted properly? Nothing clogging the fuel cap vent or petcock? etc.

 

I just looked at all the boots and made sure they were all tight. It doesnt seem to want to start now so i cant slray anything around to see if it changes how it runs to check for an air leak. One thing k noticed is i dont have the o-ring on my aftermarket fuel air screw. But i dont think that will cause enough to make it run this bad. Ill look to see if anything is clogged in the petcock and lines. It ran good when i reved it before but when i let off the gas it would die. And when i started it it would rev up and die but as long as i kept the rev up it was fine. Idk

 

I might just bring it to a local shop and have then figure out what it is thats wrong with it. Just hoping its not a boatload of money i just got layed off lol

 

Are you still getting spark at the plug?

 

Never thought to look at that. Ill have to look

 

I don't think this is the cause of your initial problem, but might be why it's not starting now.

Check for fuel, air and spark then go out from there.