just put a 396 in my convertable (originally a 307 car)engine flat out quits at 3800-4000 rpm under hard acceleration.I am running a hei distributor, changed cap,rotor,coil and wires plugs gapped at 45 no change in performance.Engine has 500 miles on a fresh rebuild runs great at other rpms starts and shuts off good.Possible valve float or am I starving engine of fuel with the factory 5/16 fuel line? graemlins/clonk.gif graemlins/angry.gif :confused: :eek: :mad: graemlins/sad.gif

Have you checked the fuel filters and float levels? I'd start there....

They are both good,carb is new also. BILL

Secondaries?

Running a full 12 volts to the HEI? Where are you getting the HEI power from?

THANK YOU ALL for your replies, full 12 volts to distributor and we have disconnected the seconderies with no success to solving problem.I have switched carbs also no change dies at same rpm.Engine is probably in the 350 horse range, when you go small block(307) to big block(350 horse 396)do you need a larger sending unit and fuel line from the tank?

anyone???

Check to see if fuel pump has return line
the the gas tank. Had the same trouble.
Return fuel line was blocked off.
Run a return line to the gas tank and took care of the problem.
Leroy

What are your cam specs? What kind of carb and tranny? Also, did you check to make sure that when you press the accelerator to the floor that the carb is wide open ( accelerator cable problem?). If you have another hei module around, try and swap it as it could be crapping out at higher rpm.