I have been plagued with this problem since I built the motor. The motor is a 400 stock bore, 256 comp cam, manifolds pretty much all stock.
Well I have a bad stumble right at 950 t 1100 rpm's. I have adjusted timing up down etc. Changed the pump cams, bigger seems crate a backfire. no difference with a smaller cam.
I reused this carb from 440, doesn't seem like I had any problems when I used them together.
Thought it might be timing, but still cant get it tuned right. Any ideas -
Oh yeah it screams after 1100 rpm's and runs great
Thanks