77 rpm issue

[Mike Koolhof]

I have a 77 GMC Sierra that starts fine, idles fine, but much over 40 mph it just won't go. Kinda thinking rebuild the carb (stock Rochester 4 bbl) which hasn't been done in a while. Anyone have suggestions other than that?
Thanks
Mike

 

[Ricko1966]

I have a 77 GMC Sierra that starts fine, idles fine, but much over 40 mph it just won't go. Kinda thinking rebuild the carb (stock Rochester 4 bbl) which hasn't been done in a while. Anyone have suggestions other than that?
Thanks
Mike

Yea,put a vacuum gauge on it,see what your vacuum readings are,don't forget to check for plugged exhaust with vacuum gauge. Drive it with the gas cap off see if the problem goes away cannister,purge line,vent issue. Check fuel pressure and volume. Check distributor advance mechanisms as well as cap and rotor condition. Check plug wire resistance end to end check all 8 looking for 1 or 2 that have abnormal readings. Check the fuel filter.

 

[PrairieDrifter]

Pull the distributor cap off and check the advance weights and springs. I bet they're sticky or rusty. Or worn out.