I'm new to this but I have a 2002 grizzly 660. It has a hmf performance series and is jetted for the exhaust. It was running fine for a while good and know it is giving all kind of trouble. It would start up and idle fine but the minute you touched the throttle it would just shut off just like you hit the kill switch but I didn't. I took to a guy who works on bikes and he couldn't find anything wrong with the carburetor or anything. He put a new carburetor and it ran fine after that. I got it back and started to run it and it started to have like a miss in just the one spot of throttle it would just start to have a miss kinda. If the motor came under a loaf or you would give it just a little bit more or just lift a little it would quite. It didn't bother me that bad so I continued to run it. It started the other day if you left it idle for like 5 to 10 minutes it would start to like miss or something weird like that and then would shut off. It was a pain to get it to start back up but you could get it and it would run but if you let it idle it would shut right off. I have it know where it won't really start up without taking a half hour of messing with the throttle and choke and it starts up and shuts right off unless you can get it to rev up and keep it up there it will stay running. Has anyone one had anything like this or similar to it. I really need help please

 

Make sure the tank breather isn't blocked, if you take the filler cap off and everything starts to work OK, it is blocked.

Change the plug.

Yams are noted for the inlet manifold leaking, you could be getting an air leak there.

If none of these cures it, you may have an electronics problem, the regulator, the coil, CDI or trigger coils going bad when warm. Check the voltage at the battery with the engine running, should be 13v to 14.5v any more and the regulator will be slow cooking the CDI.

 

Okay I will start to check and try that stuff. I will let you know if I get it fixed. I just want to add I went down a day later and it took just a little bit of messing and it started right up and idled fine. I didn't get a chance to run it. I did replace the the spark Plug wire ignition core because when I would go in a mud hole and start spinning and it would start to spit and sputtering and then shut off so we thought maybe that was bad and when the water got on it would short out but that didn't fix it and we put a new spark plug in it to. I will try and check that stuff and see what I find out. Thanks for getting back to me.