1985 chevy c10 rough running

[Dead Parrot]

One possible vacuum leak cause is the intake gaskets between the heads and intake manifold. PITA to replace but if everything else checks good, might be worth installing new. Would let you pull the lifters and put eyes on the cam lobes.

Another thing to check is your exhaust riser flapper if you still have one. If stuck shut or part shut can force too much exhaust through the intake that both causes a lot of back pressure and overheats the carb and causes it to go bad.

2nd to franken's suggestion. Look at the engine in the dark after your eyes have adjusted. Looking for sparks from the plug wires to nearby metal parts and for blue fire playing over the distributor cap.

If you haven't replaced the distributor cap, probably worth doing it and checking the ground strap connection for the coil. They sometimes get corroded. Make sure the little button in the center of the cap is in good shape.