I bought a yz426f a month ago that a shop and it was sitting for 4 months. It is giving me a couple problems but I can't seem to pinpoint it. When I brought it home I drained the tank and cleaned the carb. Also the bike is stock. To start it I have to adjust the idle every time or else it won't start. The plug is very black and the bike already fouled one previously. Also the bike backfires like crazy on decel and shoots 3in. flames. Also when I mash on the throttle at low rpms it tried to bog and die unless I let off. I know I have an exhaust leak and am ordering the gaskets for it tonight. I know the drill to start it and to never twist the throttle when not running because these bikes are temperamental. I figure the backfire is from the exhaust leak and the bike is jetted rich. I can't figure out what is causing the low rpm bog. If anyone could help me out it would be greatly appreciated.