Hey Guy's after 4.5 years, I finally drove my truck. Although it's only a 400 I'm very pleased.
Have an issue tho.. Driving normal it's great under hard accel or short WOT it will pop out the exhaust, big puff of black and buck a little like the tranny is trying to shift then it goes on.
It's a 750 holley (off of my 440) with vacc. secondaries, auto tranny. Timing seems right on easy starts after it's been driven and warmed up. I set it at about 12* stock 400 with a comp cams xe256h cam. Any ideas about which way to go - Thanks

check your total advance. I'd proabaly start at 36* @ 2500rpm. Also you really should tune the carb. Check the vaccum at idle and under load. turn the mixture screws all the way in and then out 1/4 turn. Adjust until you get the highest vacuum. Then re-set your timing full advance w/o the vacuume advance. Then re-set the carb again. It will take a few turns of the wrench.

Thanks -
On this dizzy, I don't have a vacuum advance, I think it came from a 78 or so fury or .... looked like a cop car...

Take your time, and walk away when you need to. It beats throwing wrenches down the street....

Frankly I doubt it's timing. You might have a dodgy plug wire or even a damaged / broken plug or cracked/ tracked dist. cap.

You might have weak spark, caused by a number of issues, including resistance in wiring (poor connections,) a bad coil, bad capacitor if points, or bad cap (not replaceable) if you're using electronic (ECU) Poor ignition voltage--our world famous bulkhead connector.

Also, a bad cam lobe can cause popping on one or more cylinders

Thanks - Seems to run great except for the wot - I will check all I can Though

A couple of things to check..
a. Accelerator pump stroke, adequate clearance is required
b. Position/choice of accelerator pump cam
c. Mite need to bump up the nozzle size a step

Just my $0.02..