[Pete Munroe]

Guys,

VERY SIMILAR PROBLEMS. Wll try to relate the problems.

I have a 750 Holley dbl pumper, "4779-9", on a 347 with 10.6 comp, 224/228 cam roller. rear gear is 3:54. ERA 289 car.

The carb DOES have vent whistles, no jet extensions...about 4 years old, 11,000 miles. The fuel pressure was at 8 psi...is now down to 4.5 since I got a gauge and adjusted it down. Uses an electric pump.

Floats have been up, down, and where they are supposed to be...fuel level at the edge of the site hole, maybe a little dribble if the car shakes. Performance is always the same.

OK...car in motion...

1. Slam on the brakes, the engine almost stalls as you come to a stop. I think it is going rich?...fuel sloshing in from rear float bowl?

2. Hard right turn...(turn two at Willow Springs)...steady state speed...third gear, about 3000+/- RPM engine breaks up like a popcorn maker...NAIL it as you exit the turn it pulls hard all the way to turn three right up to 6500....no problem. Front straight at Willow, about 1/2 mile, pulls like a freight train. No miss.

OK...is this problem a function of partial throttle weak vacuum signal and too large a carb for the application?

I am wondering if at ~3000 RPM I am in the range where, under load, the carb vacuum signal is causing the POWER VALVE to oscillate...rich, lean, rich, lean.

TEST to come...hope to soon having access to a 600 cfm dbl pmpr and see if the mid range response is correct.

If you read the HOLLEY formula for carb size, an engine at 350 inches and 6000 +/- rpm only needs 600 CFM...

OK, you may make more power with a 750...but drag racing normally involves a minimum of lateral G-force.

As to the Double Pumper tendency to STALL as you slam on the brakes, I have 2 other fellas with the same problem...center hung floats?...one is sloshing UP, the other is swinging down.

My side hung 1850 Holley, 580 CFM on my 67' 300hp/327" Corvette has NONE of the problems the CENTER HUNG carb on the Cobra has...the Vette is on 8 inch wide wheels so it corners fairly hard steady state.

Know that the center-hung carb is supposed to respond equally under left/right loads, but it seems inherently challenged by acceleration/decelleration...LOOKS COOL...but other than that...?

Pete