I am in need of any ones expertise on a ‘73 Corvette. It is an L82; 350 that is fairly stock as far as I can tell (new purchase). A problem that I am having is a back fire or miss fire in the motor at about 3000 rpm under load with no power gain; the rpm’s will slowly increase with no power. I was thinking that it might be an electrical problem; I have checked the cylinder compression (145-150) timing, dwell, spark plugs, sparkplug wires, coil, cap, rotor and points with no change.

I have replaced original distributor with new MSD parts; distributor, cap, rotor, wires, coil, ignition control and new platinum spark plugs. There is a significant power and throttle increase at the lower end, the problem still exists with a slight increase in rpm (3500).

After exhausting the electrical probability, I moved on to possible valve springs sticking or weak. Removed valve covers with no visible issues and checked tension on springs with no noticeable difference. Next moving onto fuel, when I replaced the fuel filter, it had another increase of about 500 rpm totaling it to around 4000 rpm. Old fuel filter had some rust and junk in it so I looked into the fuel system further finding rust and some thick gel substance (probably from fiber glass from trying to repair tank, previous owner) in the tank. Next I tried a MacGyver stunt till the new tank shows up. Took a new electronic fuel pump and a gas can (seat belted in of course) and a fuel line straight to the carburetor(s) bypassing all old fuel lines. I have tried three different carburetors (rebuilt Holley 650, new Holley 650 street avenger and Rochester Quadra jet) with no real change.

I am stuck and need some help. Do I need to rebuild or am I over looking the simple solution? Sorry for the long story. Thank you in advance.

 

What exactly happens at 3000 rpms,..starts to miss? bucks? or just wont rev past 3000 as if it has a governor?

 

It may be your cam shaft gear. They used gears that were coated with a composite type material to reduce engine noise. When the material wears or breaks this can happen. My 73 had 89K miles and the gear was shot, had similar symptoms. Good luck.