Thread: engine surge!

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Hello everyone! I am new to your club, I stumbled across it while cruizin.
I have a question maybe you can help me with. I have a 70 mustang, I call her my baby, she has developed what I call an engine surge. At idle the motor will hunt and surge. It is very rythmic and the rpm will vary between 300 - 700. When I accelerate the motor will stutter briefly then between 2500 -3500 rpm I can feel her surging as well. At about 4000 rpm it seems to stop, but I truly cannot tell. I have good oil pres at throttle 68psi, my fuel pres seems good as well. I checked all of my vacuum lines, the plugs are all connected, the wires seem fine, and my timing is about 3-4 deg advanced.
The motor is a 351 cleveland with a Holley 600 4bbl that flows 900cfm.
Honestly, I feel the motor is not getting enough air, but I am only guessing

Any help would be great. I apologize if this is a repeat topic.

900 Cfm is probably away to big for your engine. You'd have to be making something like 900 hp with a 351 to need a 900 cfm carburetor.

Kinda sounds like a blown powervalve in the carb. Easy ck. is to screw the idle screws in. If it'll run with the idle mixture screws 0-1/4 turn out the powervalve is blown sucking fuel directly into the engine. Most 600's idle great with the mixture screw 1-1.25 turns out.

Another thing, 3-4 degs. initial advance seems low. How much is the centrifugal adding and at what rpm's does it total out? Is the vacuum advance working? (while you've got the light hooked up
)

Thanks for the replies.

The motor was built in 97 by a former indy car mech. circa 1960s, he was the one who made the carb flow like that. I have about 10k on the motor, I just started driving it again after it sat for awhile

Unfortunately, I am not that mech inclined I can destroy stuff, but putting all back together is another story. Anyway, I will try the idle screws, but what is a powervalve and what does it look like, where is it on the carb. As far as the total advance I am lost. I can time the motor, but I could not tell you what the centrifugal is at what it totals out at.
The car does not backfire through the carb, but it backfires alot when I drive it. I am not sure if it has an anti blowback valve. The pcv valve is metal, and I have not sniffed the oil.

Hey thanks for your initial help, anything else you can provide would be great.