piston slap plus carb backfire -- Help!

[Steve]

Hey everyone. When I start the bike up -- Mastiff '07 (past 4 times was when it was cold) I get a backfire up through the carb and a pretty heavy piston slap -- sounds like the pistons going to break it hits so hard. Does anyone have any idea what it could be and what I could try for a fix?. Not a big time wrencher but I'm willing to give anything a shot. TIA.
Steve.

 

[MARV]

pull the plugs.

i bet they're cooked from running lean.

 

[woodbutcher]

piston slap or compression kickback. not a guarantee but make sure your compression releases are manually depressed. might help. this is what i do.

also, listen to marv.

 

[lee]

the bang could be the jackshaft hitting the ring gear?