Adjust your lifters, so you are absolutely certain they are within lash spec for your cam manufacturer.
Check for lose rocker adjustment studs?
Look for threads are worn and the stock crush lock nut is not worn out and rotating under vibration.
Sometimes they loosen up and that can throw a valve or bend a pushrod, left unattended.
Check for the green rubber three striped o-ring at the ignition module connector, if you have a weatherpack connector to your distributor housing. Sometimes moisture get unders the cap and the heat sink past on the ignition module dries out.
If the module has 4500 ohms instead of 5000 ohms, it's bad. Only ones I can get to work are ACDelco.
Same with wires, as already suggested.
Plug check will tell you a lot, if one's not brown like the others should be.
The NON-ACDelco wires have been the cause of my stumbles with OBD1.
Ignition module failure from a leaking connector and bad ohms, as well.
If one of your rockers has lossened up and the hreads are sloppy for standard lock nuts, you might want to invest in some taller covers with poly-locks, so they stay put, once you set them.
That backfire could bend something or start a fire out the carb, if you don't find it.
Check you cap and rotor for corrosion and loose screws too.
Last thing if everything else seems OK:
If you burn corn fuel, E-15, E-55 or E-85, the carb fuel ports and venturies could be clogged and use a good cleaning?
If it's a well used carb, you could have a leak at the throttle shaft bushings or a squirter is dripping.
Worn casting or bad bronz bushing on the throttle shaft?
Spray the carb casing and the vacuum ports and listen for idle improvement?
Try soaking ithe carb and check the orofices with a set of acetalene tip cleaners, if the throttle shaft is indeed still sealed and not the leak. Meybe a chunk of crud is partially blocking a vacuum port on the carb?
You could have a pinhole leak in the accellerator pump gasket or the carb base gasket leaking.
This usually causes idle issues.
I have heard of a chunk of casting flash inside the carb chambers causing this issue.
If you have smog system attached, anything in that mess could be suspect as well.
Let's hope that it just wants a new set of ACDelco wires.
