Help Me!

[EXinMB]

I got a 2002 400ex that is completely stock as far as engine, carb, exhaust goes. Now this thing backfires after I go from like 5th gear tapped and go into a corner. High rpm to low it backfires. if i keep giving it a bit of gas it won't backfire but as soon as I let go completely, bang. Also it burns a lot of oil too.

so, jetting and needs new piston rings? i have searched the net and cant find answers:confused:

[underpowered]

Sounds like your pilot jet is clogged. clean your carb to resolve the backfireing.

burning oil could be rings, probably is if it si a stock 02. could also be your valves seals, which should be replaced when you re-do the top end.