'85 K20, 350/400/208 124k miles. Ok, I just rebuilt my carb cuz it was pretty bad (VERY rich). Now I'm gettin about 14mpg. It runs awesome,, idle mixture is set perfect, idles awesome has ALOT more power. Problem is when I get on it pretty heavy then let off it backfires out the pipes and sometimes theres a little flame, which tells me there are unburnt vapors (obviously) and possibly a lean mixture could explain it running "hot" enough to ignite. As usual I used a vacuum gauge to do the idle mixture and set it to the highest I could get with it still idling good, 17 inches of vacuum on both sides. I have no cat, dual flowmaster 40's out the side. Initial Timing is set at 6*. I'm runnin Delco R44T's and new wires,cap and rotor. New float, everything in the rebuild kit was used where applicable. Also, I epoxied the main wells before I put it back together, they were pouring fuel down the intake pretty badly. lol. I did have to swap out the base becuase the secondary shaft was a little wore out but reset the idle mixture. Everything is functional on the carb. It wasnt doing this before I rebuilt the carb so something isnt set right, what are some things I should look at?