My nephew has a 110cc Chinese quad. Don't know what brand it it since his parents bought it new for him & the dealer is out of business. The engine looks like a Yamaha engine. He has run the fire out of this quad the 2 years he has had it with no problems. Last weekend he rode it all day long, went through a full tank of gas. I refilled the gas tank & he rode a couple more hours then it quit. It is getting spark but I thought it was starving for gas so I replaced the fuel filter with a lawn mower filter. He rode it about 15 minutes & it quit, like if you shut it off. Starts right up after a couple minute but quits again when he starts riding it.
My wife & I have own a 200cc & a 250cc Hi Birds for 3 years, have run them rough, & have had no trouble out of them. I don't know how to diagnose my nephew's quad problem. Any suggestions will be appreciated.
Thanks,
Jerry

 

Not sure if it has one but maybe a clogged gas tank vent hose?

 

It sounds like your running out of fuel at high engine speed. If the fuel feed line can't provide enough fuel at high speed then the float bowl will eventually run dry. When the engine has stopped the float bowl fills back up and the cycle repeats.

A clogged gas tank vent will do this (as Vicdog said). So will a clogged/resistricted/defective fuel filter, a defective fuel petcock shutoff valve, or a needle valve in the carburetor that won't open all the way.

Remove the fuel inlet line to the carburetor and fill a cup with fuel. See if the fuel gushes out or comes out in a weak dribble. If it dribbles then loosen the gas cap and see if it improves.

 

When I replaced the fuel filter, gas rushed out of the gas line, this quad doesn't have a petcock or fuel shut off valve. I had the problem with gas cap not venting on my Hi Birds but this one is venting good. Even through the fuel filter, gas just pours out. When I first checked the spark plug, the spark looked weak & then I checked it again a few minutes later & it looked strong. When it quits running it's like you hit the kill switch, just stops quickly. Let it sit for 2-3 minutes & it starts right up & runs for a while then stops again. It's almost as if the spark plug quits firing. The carb seems to have plenty of gas in it. Like I said, this kid's run the hell out of this quad. He's 11 years old & rough on it. Thank you for all your help.
Jerry

 

I had two quads fail with fuel delivery problems, and the symptoms were just like you described - riding along fine and then the engine quits suddenly, and starts up a minute later. I wouldn't discount that quite yet.

If it is an ignition problem you could ride around with a spare spark plug. Then when it quits you could quickly switch the spark plug wire to the spare plug and check for spark. That would isolate whether it is an electrical problem or not.

Jaster94 posted a good idea on another thread about fuel delivery problems (at least I think it was him... ) where he suggested that the fuel petcock valve be shut off right as the quad quits. Then you could check the float bowl to see if gas is in it or not. Of course you would need to add a petcock valve, which you really should have anyway.