I recently purchased a leftover 650 H1. It runs fine a high speed but when running at low speeds and especially slowly going down a hill it tends to back fire and will just sit and idle. When I press the throttle it won't accelerate and wants to die.
I changed the plug to a NKG and blew out the vent hose to the gas tank. Still has the same symptons. I'm thinking maybe the slow speed jet was not adjusted correctly. Any ideas. Also, does anyone have the setting for a slow speed jet for the 650 H1. I'm assuming it's so many turns out.

 

Bad Gas?? - maybe

 

Trailbalzer, I played with the slow speed jet screw and it seems to be ok now. I still need the correct setting for a 2008 AC 650 on that screw. Also, these companies are now using a srew head which requires a special tool. Its shaped like a D.