Ok guys, I have 4 of these things, all running good except this last project. I've been through just about everything on them but i'm pretty stumped on this one probably due to not spending enough time yet. The quad will start. Starts very easily actually by pull start. It revs to idle then it immedietly cuts off. Most are going to think carb issue, NO. I swapped carbs from another quad that is turn key running idling good and runs like a raped ape. So. What I have found is that if I choke the air off, either stuffing the air box full of rags or closing the air off it will idle. Will not take throttle though. I have gone as far as popping the magneto off and changing the sheer key as I have had this be a common problem with these. Still did not change how it runs. Magneto looked good inside. I have not popped the rocker cover off and checked to see if it jumped time a tooth or so but why would it run at all if that was the case, and start so easily? Just wondering. I'm going to check that tomorrow. I have checked all wiring, wouldn't be that if it will run I guess. As I said it will run with the air box stuffed up, and I have swapped carbs. Not sure what else it could be. Havn't done a compression test but I wouldn't think it would immedietly pull start if it was down on compression either. Feels tight enough. Anyone got an easy button on this one?

Moto

 

its lean somewhere. thats why it idles with the airbox cutting off air. do you have a clean and charged air filter with the air box lid to go on it? or check for a cracked intake boot

 

I agree that it's probably an air leak. Try spraying Ether around the air boot while it's idling. If it revs up, you've got an air leak.

Another thing to check is the CDI, although that wouldn't explain why it idles when you plug up the air intake. Still, it's something to check that goes bad on these bikes. When they go bad, they don't always just quit completely. Sometimes the bike will still idle and run a little. If I were you, Id swap one from one of your other bikes that runs good to see if it helps.

 

Thanks for the input everyone, I got it running perfect today. There was a rub on one of the wires and I guess it didn't totally kill the spark but it would not ark as much at idle but once the motor fired up it was grounding out. Had to hang stuff I'm the garage and get it pitch dark to catch it but man it runs like brand new and starts so easily. I appreciate everyone giving me feedback. Three down one more to go lol. I love these old runners I used to race 450s but yhad a bad accident at a national in west Virginia two years ago and had to have my knee replaced so they are more my speed. Thanks again everyone.