I volunteered to fix my neighbors sons quad. It has a 72cc loncin engine and was made in 06. The original prblem was a broken fuse under the seat. After that was fixed it ran as usual with my son testing it for about two minutes. The next day right before I took it back it wouldn't start and when it finally did it seems to miss 70-80% of the time. It will not try to start (or run) on choke at all. So far I totally disassembled and cleaned and adjusted the carb , adjusted valve clearance , swapped out the cdi , coil , the other black box with the green connector , spark plug , and the stator from another running 70cc quad. I also ran it with the exhaust removed to make sure it wasn't clogged. I also tried grounding out the one wire on the coil to make sure the ground was good. The only odd thing I notice about this machine is that the stator rubs on the rotor causing it to scrape some. I put a small amout of grease on it to help it. It surges when it fires correctly and then tries to stall(several times a second). it also doesn't smoke at all when it runs. I appreciate any thoughts you guys may have. I am at wits end and can not return the kids quad not running.

 

Got the title fixed for you.

Hopefully someone can help you get it back running properly.

 

Almost sounds like it somehow the timing has been knocked off.