Need help

I have a gm 350 stroked to 383 with a holley carb. When crusing at 4000 rpm the boat runs fine but anything over 4200 it starts to backfire or popping the engine builder said we can get upto 5200 rpm I don't know what to do to fix this problem any help would be very usefull

 

Fuel starvation. Check out all fuel lines, filters, breathers, pump etc etc

 

saabster

try increasing your fuel line size.i hav a 350 tuned up to 330hp, increased fuel line to 12mm. runs brillant.

 

Fuel starving sounds good to me too.
I also wonder about the Points bouncing. Do you have a Breaker Point distributor?

 

Hmmmm

Backfiring intermittently sounds more like ignition than fuel. Fuel starvation = too lean, right? Usually a leaned out engine smoothly loses power. Unless the lean mixture causes preignition, maybe.

Fuel filters clean?

What do the plugs look like if you shut down after running at 4000 for a while, and pull a couple plugs?

Is this a Holley 2-barrel? I have one on my 350. If I shut the fuel pump off, the engine surges and loses power before stopping. But it doesn't pop and backfire...