Backfiring through carb/air cleaner

[moperformance]

Hello,
69 Superbee, 383, 4sp, 6 pack. On the 2005 power tour at the upper end of rpm range it would start to pop/back fire through air cleaner. Pretty much wrote it off to leaning out and tried not to push it that hard. Jump forward to now and the car has been sitting 3 years waiting for me to finish the 4speed conversion. Conversion was finished couple months back and on the first drive it started popping through the air cleaner real bad at 4 grand if that. I've driven the car to Ga to skin the roof and stopped after about 30 minutes and advanced the timing because the car was running 205 and you couldn't get passed 55 mph. after the advance is will run 75mph but every once and a while it will pop back through the air cleaner I have checked for vacuum leaks, etc. Any thoughts would be greatly appreciated!
Thanks,

 

[TS5064]

do a leak down test on it. sounds like your valve springs are week. sounds like your going to need to pull the heads. replace the springs and do a valve job on them why it's apart. or you could just replace the springs on the motor if you have the tools to do it. { nice looken bee }

 

[Meep-Meep]

You might also check to see if your dist cap is carbon tracked or maybe just replace it. Bad plug wires can cause problems also.

 

[SUPERSTOCKRACER]

last time i heard that was when i leaned out a motor and blew a head gasket. check your plugs and see if they are white. sounds like a very lean condition.

 

[70rr-brian]

Possible worn cam lobe?

 

[moperformance]

Thanks for ever ones input! The only one I can rule out is the carbon tracking as the cap (MSD) was replaced first thing along with the wires. Also sprayed carb cleaner around intake, carb, etc. with no increase in RPM
Regards,

 

[earlytime]

I had backfiring with my carb, and I got it started after about 1/2 hr. I then sprayed carb cleaner around the intake and the passanger side has a big vacum leak. So now I'll replace the gaskets here soon. mike