I share what I know of the pumps need
at idle the car uses the idle circuit.
once your off the idle circuit and the throttle plates are open if the motor does not have enough vacuum there is no way for the gas to get into the motor
the pump gives a quick squirt till the vacuum catches up to pull the gas in
car in park or neutral (No load) race the motor and you get no stumble you could still have enough vacuum to make you believe you dont have a problem with fuel
Car in gear race the motor (under load) this is the real test as if you have the stumble it could be the pump, or undersized squirters, or clogged squirters
What actually happening with the car?
Well to the best of my abiliities, I've done just as you say but it continues to stumble at the higher rpm range. I'm about to take the carb apart again and examine the the pump. Might even put the old one back in since I didn't have this particular problem before the rebuild.The only issue I ever see is accelerator pumps that are improperly adjusted; the .015" clearance adjustment is made with the throttle lever at WIDE-OPEN THROTTLE position, and with the pump operating arm depressed. Takes three hands or a good rubber band, but it MUST be done that way.
Well to the best of my abiliities, I've done just as you say but it continues to stumble at the higher rpm range. I'm about to take the carb apart again and examine the the pump. Might even put the old one back in since I didn't have this particular problem before the rebuild.
It stumbles or pauses when I hit the gas from a stop or rolling stop. Seems to run okay from there until I really step on it when cruising at 55 mph. I've checked the timing, changed the spark plugs and plug wires, and adjusted the floats. I suppose I could change the points and condensor next.I hope I can explain this correct
When you say high RPMS the pump only gets you towards higher rpms when you hit the gas.
Once your at high rpms and you have a miss, its not from the pump.The pump is only used to get you toward higher rpms.
Once you have flow thru the carb (air) then the air/vacum takes over on pulling the fuel into the motor.
How is the ignition system on the car,
I just returned from a 10 minute drive. Here's a better description of what's happening.Brumbach,
Like IH2Lose said, your pump cam could need replacement with a different cam profile; however, not knowing what the problem is on your Vette is troubleshooting this issue back-wards.
You see, for sag or hesitation during light acceleration, one must look at the following:
- Intake [manifold] leaks
- bad fuel
- clogged air bleeds or passages [perhaps not likely at all since you just
completely rebuilt the carb]
- leaky or disconnected distributor vacuum advance line
- wrong initial timing setting
- acceleration pump defective [ perhaps, as I stated above, the pump cam is probably not the best profile for your engine settings right now (i.e. the cam, CR, timing settings)
- clogged idle transfer slots/ holes (you did clean all of the parts...right?]
- if after all of the above items check-out fine, then perhaps you have too-large of a carb for your engine.
Returning to the cam profile, one must understand that the pump shot on Holleys is needed to help the engine go from the idle system to the main system (there are other purposes as well), so the cam profile can be changed to adjust how soon or how late the shot is delivered. Too soon, and you won't have fuel to sustain the acceleration of air through the venturi. This will result on a lean condition, and a backfire will develop. Deliver the shot late, and you'll feel hesitation or a lag in acceleration.
p.s. I forgot to mention that the pump cam profiles also adjust the amount of fuel is delivered for that particular cam.
The only issue I ever see is accelerator pumps that are improperly adjusted; the .015" clearance adjustment is made with the throttle lever at WIDE-OPEN THROTTLE position, and with the pump operating arm depressed. Takes three hands or a good rubber band, but it MUST be done that way.