The setup is as follows.

355
234/244 .488/.510 114 lsa
Holley 4160 750 Vac Secondaries
Holley black label Mech. fuel pump
Torker II intake (single plane)
World SR heads (unsure on valve size)
Hooker long tubes into 3" single w/ cutout
Full MSD Ignition
700R4 Trans w/2500 B&M holeshot converter (going to Pro Yank 3600E)
3.73 open diff. 10 bolt (going to 3.55 9")

Problem is I had the carb tuned decent, then it just went to crap. Now under a load it backfires through the intake.

Have not rechecked for any vacuum leaks yet, just want to make sure the setup is somewhat close. I can only get the vac. guage up to 8 or 9 when setting idle mixture.

15 deg. base timing, 38 total at 3200 Mech. adv. only
Primary Jets - 72
Secondary plate 21 (75 jet)
Pump discharge - .025
Primary power valve - 65
Secondary spring - Plain Silver
Took out the Orange pump cam and put in the blue on hole #2.

 

Is the vacuum gage steady at idle, or does it bounce around a lot?

 

Bounces like a super ball.

 

Sticking or leaking intake valve. Nothing to do with the carb.

Do a compression check to verify.

 

Broken valve spring.

 

150 on all cylinders except for #1.

Valve covers will be coming off later this week and then I'll be back to the carb.

Thanks guys.