My C3 1976 Corvette runs very well under 60 miles per hour. However, when I hit above 55 miles per hour. I will be pressing the gas peddle and it sounds like my corvette is not getting gas to the engine. It will accelerate and stop accelerating while I am pressing the gas peddle going above 55 miles per hour on the interstate. Does this make sense? I am an amateur when it comes to working on cars. In matter of fact I have been paying a mechanic to fix my car. Does anyone know what I have to do to fix this?
I have replaced the fuel pump already.
Does my engine need to be rebuilt?
Like I said it only acts up at 55mph to 60 mph plus.

What part of the motor is in charge of going high speeds?
What all should I get looked at?
What all should I get replaced?

 

Little fuel filter on the front of the carb. Ignition timing. Bad vacuum advance can. Carb rebuild or replace. YouTube is your friend. Tons of info and you don't have to wait for answers. Getting a 350 to run good is not Corvette specific. He'll, it isn't really even Chevy specific. But start with the cheap stuff like timing and filters and plugs, wires, etc before you start buying engines.

 

The vacuum canister is not involved with throttle positions of the higher speeds / RPMs
Could be the fuel sock strainer in the gas tank.
A fuel pump that is getting tired already? (diaphragm)
Or a IGN Coil or Module that can no longer keep up with the RPMs.

 

Rubber hose on gas line can deteriorate and flaps can close off supply. Cheap enough to change any you may have

 

You paid your mechanic to fix the problem and he changed the fuel pump. Did he test drive the car to see whether he resolved the problem rather than you having to guess what the problem is?
Other than change the fuel pump what else did your mechanic check?

 

i suspect too much timing from either springs on adv weights or
plus vacuum can.

 

Heads-up is probably right. Vac advance doesn't really effect power. It is for light load economy. But too retarded in general will cost a lot of power. Bellau: Does it feel like running out of gas? Cutting out and running again? Or just overall weak. A fuel flow problem and it willpractically shut off and catch again when enough fuel fills the bowl. And you are talking half throttle drivability, not full throttle max acceleration?

 

You say it runs fine under 60. Does that means it accelerates hard, but only up to 55? What happens if you're in a lower gear? Is the car smooth but slow? Or does it miss like it's running on 5 or 6 cylinders? You need to think about what's going on and how it would affect your issue. If it's starving for fuel due to a clogged filter, etc. it's getting fuel, but only at a reduced rate. So if you sat idling at a stop, your fuel bowl will fill eventually, then if you got on it, it would accelerate fine until the demand outstripped the supply and it would starve for fuel, maybe at 55 mph. Then it would just about die, but eventually run again. If you accelerated gently and kept the demand within the supply, maybe the demand equals your restricted supply, at 55 mph. If this seems like your problem, do the following. Disconnect your fuel line at the carb entrance. Have someone start the car and see if you get strong surges of fuel. If not, you have some clog or restriction along the way. If you do, check the little filter in the carb, if its ok, your problem lies maybe in the carb itself or elsewhere. Maybe your float level is way too low. But don't just throw parts and money at the problem, Use common sense, check the free stuff first: ignition, point gap, timing, plugs and wires, compression, vacuum leaks etc. You'll save money and its more rewarding if you learn how to do some if these things yourself. These old cars don't ask for much, and the people on this forum are very helpful, but like visiting a doctor, don't just say it hurts, but how when and where does it hurt.

 

I bought an Edelbroclk 600 CFM Performance carburetor from Ecklers corvette. I helped install it. My motor no longer chokes when going high speeds any more. I am very satisfied. I recently bought a Edelbrock Performer EPS Intake Manifold. I will be installing that Performance Intake Manifold later this week. I am hoping that this intake manifold will allow my car to accelerate faster!