I have a 2005 650V2 and have developed an issue I can't figure out. When I try to start the machine (cold start) with the push button electric starter it cranks but won't fire. Sometimes it will fire and just barely idle but when I try to hit the thumb throttle it dies. If I continue trying to start it with the push button (about 10 minutes worth of cranking) I can then use the recoil starter and it fires right up and runs great. What I mean by barely idling is it just seems like it's barely running if that makes any sense. When I start it with the recoil starter it has a much stronger idle and will not cut off when I hit the thumb throttle.
Once the atv has been running and is warmed up I can shut it off and start it with the recoil starter without any problems but the push button starter still won't start the machine. I thought it might have something to do with the crappy choke that came on the 2005 model but that doesn't make any sense if it starts with the recoil starter. Any ideas???

 

I had the same trouble with my 650 v2. I had to adjust the valves and it starts fine now. when it's cold I had to use the rope start but after it warmed up it would start fine with the electric start.

 

Check valves as mentioned, load test battery, clean / regap- replace spark plugs . It could be battery is strong enough to spin starter but not strong enough to spin starter AND fire plugs.