Recently swapped a 406ci sbc into my 84. Quick fuel slayer 750 carb and msd 6al ignition. The car runs great at idle and normal driving. When I get on it hard it runs like a raped ape but as soon as I let off the throttle it stumbles and stalls when im slowing down. The only way I can keep it running is to quickly shift to neutral and rev it but even then it stalls alot of the time. Im at a loss, any ideas of what I should look at?

 

Fuel bowl empty? i.e. float needs adjustment?
Spark box got a problem? Disconnect it and test.
Linkage for the 4bbl getting hung up and holding open when it shouldn't?

 

Sounds to me like it's flooding out. Assuming that's a double pumper carb and If your braking when it happens, then check your rear discharge nozzle(squirter) pump arm for proper clearance. It would need adjusted so that it doesn't keep open/cracked/unseated all the time. Basically slowing down dumps fuel from the rear nozzle.