Car hesitates and backfires when I start moving from idle, sometimes even stalls. Seems that I hear the backfire from the exhaust, when it stalls it definitely backfires through the carb. When I shut the warm engine down after some intensive driving, it backfires once through the exhaust.
It works nicely once I manage to get it moving from start.

It is a 350 with stock bottom end, Trick Flow 30400001 heads, Edelbrock 2102 cam, Weiand 142 blower and Holley 4165 (6210-3) 650cfm double pumper carb. It is a spreadbore carb with mechanical secondaries. I have jetted it up 5 sizes in primaries and 8 sizes in secondaries from where I was before installing a blower, to keep it in safe side.
Carb is not boost referenced. I know that 650cfm is not enough for a blower and I am probably losing some power.
The ignition is set to 6 degrees initial advance and 28 degrees total, the vacuum advance is not currently connected at all.

I have tried changing power valves from 6,5 to 8,5 to 10,5 with no difference. Unfortunately I do not currently have a possibility to check the AF ratio under load. Where should I start from before melting the pistons?

Upgrade 30cc primary side accelerator pump into 50cc? Boost reference the carb? Change jetting? Increase the size of the power valve channel restrictions? Replace the stock fuel pump with an aftermarket one? Check the ignition instead of fuel delivery? Any other ideas?

Thank you!

 

ign timming?

 

I know nothing about your topic here (that carb, and the forced induction), but I really think a non boost referenced carb wouldn't work for you. Can someone confirm this?

How's it run at cruise? If it's really rich/lean, jet the primaries so that's right, then re-check your idle mixture, and your throttle plate position. (I'm a q-jet guy, so this might be totally out to lunch. ) Anyway, that's my
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sorry, re-read your post. Remove the easiest to get to spark plug, clean it up, or replace it. (your spark plugs have a smaller gap due to the blower right?). Cruise down the road, for 5 minutes, constant throttle position, constant slope of road, etc. pop it into neutral and shut it off and coast to a stop on the side of the road. Pull your plug and check it. There's your cruise mixture. Jet accordingly.

Post cams specs, but I think you'll need more timing at idle, then close your throttle blades.