backfire out of carb

[trxPOWER]

hey guys i just got done building my 440, and the thing runs great with tons of power. As to my problem. Off of idle it backfires out the carb, but thats the only time it dose it. i looked at my plug and it is black. It has a 168 main jet and a stock pilot jet(38) the (pilot?) screw is tuned all of the way in. this is baffling me. Could the problem be valves are out of spec? thanks for any help.

[Pipeless416]

Originally posted by trxPOWER
hey guys i just got done building my 440, and the thing runs great with tons of power. As to my problem. Off of idle it backfires out the carb, but thats the only time it dose it. i looked at my plug and it is black. It has a 168 main jet and a stock pilot jet(38) the (pilot?) screw is tuned all of the way in. this is baffling me. Could the problem be valves are out of spec? thanks for any help.

sounds like you're way lean on the pilot. try upping it to at least a 40 and your A/F screw should not be turned in all the way.. try backing it out to about 2.5 turns and see where that gets you.