1971 Chevy truck chugs at low RPM

Driving steady in 3rd gear at 2000 rpm causes truck to chug, almost like I’m giving it gas and then letting off. Acceleration resolves the issue. The truck drives great otherwise. It has a 350 engine with HEI, just replaced the core, cap and rotor, plugs and wires, fuel pump, and gas tank. It has an Edelbrock 600cfm auto choke carburetor that I put on maybe 15 years ago. Went through it a couple times over the years with the little rebuild kit you can buy for it. I am stumped and am wondering if I need to replace the carburetor or check for vacuum leaks? I don’t know much about vacuum. I sprayed some carb cleaner around the manifold and the carb at warmup but didn’t really notice anything, and wasn’t sure if I got it in all the right spots. Any ideas?

Have you’ve checked for a stretched timing chain?


Checking the timing and dwell angle or point gap if applicable could be helpful.

I have not checked the timing chain. The timing is at 8 degrees btdc, and it no longer has points since I put in the HEI. Does the timing chain sound like a reasonable culprit? I will start pulling things apart if it seems the likely cause.

You don’t need to pull things apart to check for a stretched timing chain.

Remove the distributor cap. Have someone get on the crankshaft bolt with a socket/breaker bar. Turn the engine by hand in one direction. While watching the rotor in the distributor, turn the engine in opposite direction. The rotor in the distributor should also turn as soon as the crankshaft is turned. If the crankshaft can be turned 5? or more before the rotor in the distributor starts turning, the timing chain is stretched.


Oh nice, thank you. I will go try that now.

The chain appears to be fine. The rotor turned without any hesitation in both directions.