Lars recommends starting at 3/8" for a street vette. My rebuild kit instructions list 1/4". I trust him, but I compromised and set it to 5/16". However, I think I’m getting a high rpm stumble at the very top of 2nd gear. Could the bowl be running empty? I have fairly new pump and filter installed.

Is 3/8” ideal for smallblocks? Mine is a BB.

Could something else be suspect? Engine is stock, including the jetting. If I raise the float to 1/4”, what do I lose in terms of drivability and mileage?

 

Turbo -
I run all 1967-1974 Q-Jets at 3/8" - even the BB carbs. This reduces the amount of fuel slosh out of the accel pump rod hole, and reduces gasket wetting of the airhorn gasket. It also tends to produce a little better throttle response off idle. I've never had the 3/8 float setting contribute to a high-rpm stumble, and the float bowl fuel level should remain at the setting if fuel supply is not a problem.

Normally, this type of a stumble can be attributed to the following possible issues:

Secondary airvalve spring windup too loose or too tight (should be 3/4 turn)
Incorrect secondary rod hanger height (should be .640")
Lean secondary rods (check against spec)
Power piston remaining in full lean condition (stuck)
Incorrect primary rods or jets (check against spec)
Incorrect type of float (use a NAPA 2-440)
Airhorn not sealing to the float bowl in the secondary fuel passage transfer area (warped airhorn)
Restriction in fuel line (kinked rubber hose at the tank or at the pump)
In-line fuel filter installed on suction sude of pump
Restrictive filter "sock" in fuel tank
Incorrect timing setup or other ignition related problem
Low pump pressure

 

thanks! i will check the sock first.