This makes no sense to me, so I will ask your opinions. I had a 650 Holley dual feed on my car, it bogged bad of the line and would cough through the carb in certain situations. I threw a 600 on and that was no good too, then I threw a 750 double pump dual feed on. I had perfect throttle response, and it does not pop. The strangest thing to me is that it is a mechanical secondary carb, yet when I floor it I dont drown the motor. I still have the 307 in it, so motor should be way overcarbed now, but it isnt, any idea why?

 

depends on the jets in the carb, weight of the vehicle, intake runner size, and other varibles. there is no clean cut answer. Sick

 

well the heads have a 2.02 intake valve, the cam is pretty small, since its on a small cube motor, and as for the carb, it came off my buddys torino with a 390 and a lotta cam, so its not set up for a small motor, he did say it ran a little lean on his car, but not much. as for weight, basic 71 camaro, weighs like 3600 pounds or thereabouts

 

[&:] any carb is nearly infinitely adjustable but what you describe probably speeks more to the condition and tune of the carb than the cfm. coughing thru the carb is often a sign of a lean condition. the car is overcarbed a 750 is way big for mild small displacement mouse motors. id say that this latest carb is probably tuned closer to the needs of your motor and in better repair than the last ones, thats why less problems. however if u actually dynoed this setup i would guarantee that if the smaller carbs were tuned properly they would produce more power across a wider rpm range than the 750. you can make(adjust/tune) almost any carb work in alot of mismatched situations but you will not realize the HP potential of the properly sized and tuned carb kurt

 

thats what I thought too, but the 600 we put on was dead through the powerband and the 650 that came off we played with forever trying to get it right. The biggest surprise to me, and the thing I dont understand is from idle Ifloor it, and the carb is mechanical secondary, so they are def opening up, yet it doesnt drown the motor. My 650 was jetted down considerably, yet it would nearly drown it out, thats what I dont get

 

Clearly your 650 had a problem. Lean jets, blown powervalve, vacuum leak or whatever. That being said I never met a 750 I didn't like.

It's probably a little too big but as long as you don't foul the plugs or blow black smoke I would stick to the 750. (Just for fun you should try an 850)

 

I think I had power valve issues in it, I replaced it once when I rebuilt the carb, but I think it must have gone bad again.

 

[8D] if the 750 is a double pumper it will certainly help avoid the off idle cough or hesitation when you mash on the gas as its designed to dump extra fuel into the secondaries as they open as well. holleys are notorious for power valve problems.

did the 650 drown it out or did it go lean, when you hit the throttle?? either way it obviously isnt right. the 600 or 650 is still a way better choice but if you dont have the ability or knowledge time or money to make the necessary repairs or adjustments to them then stick with the working 750 but you will be denying yourself some responsiveness and horsepower kurt

 

I had used a holly 450 CFM on a Pony 302, and with it tuned and jetted properly, it has been the best set up I have ever used. Hollys are very tempermental, I have had great luck with Edelbrock (Carter AFB) carbs. The metering rods are easy to change. I used a 750 CFM on a BB 455 I had in my 81 Trans Am. The pure power it produced was nasty. Also, dont ever underestimate the qualities of a quadrajet.New, they are very resonably priced, and the junk yards are full of them.Pick one up for $20, and have a pro rebuild it for short money. Or get a rebuild kit and D.I.Y.