I need to hit it with the timing light again.

The car just recently started back firing through the carb as soon as the secondaries kick open. It will pop, have a milisecond bog, then the car runs like it always use to.
Before, the transition to secondaries was smooth. Now it pops, and then hauls ass.

So i am looking at the fuel delivery right now. The bowls are set right in the middle, and i just rebuilt the Demon.

Motor is 496 roller
11:1 static
MSD HEI with 6AL
Pro Topline Heads 320's with worked 11/32 valve stems
Demon 850 Mech. Sec
Timing right now is set at 10.....I will post total timing tonight.
110 low lead race fuel mixed with 93 from the pumps (60% leaded with 40% pump)
I use to have 12 degrees in the motor with strictly race fuel, but it would detonate through the intake. I rolled it out to 10 and now it only does it at a heavy load. IF i gently and gradually put the pedal to the floor, it runs great. But if i floor it from a stop, or a slow roll it pops, bogs, and then boils the tires and its like the car is on glass.

I used to have this thing running 10.80's with 10.5's out back and my CalTracs. Now she is kinda sick.

So I am going to check fuel pressure at about 3,000 rpm on the road. So i will start there.

any other ideas would be great
thanks guys