1973 Mustang 210hp 302.At idle it acts like I have an air conditioner(I don't).Every few seconds the engine slows & runs like crap,small backfires out the exhaust,then straightens up for a few seconds,then runs crappy again like an older car w/an A/C.
I still have the original distributor w/points and the external voltage regulator..Any ideas?

 

Check the points for their condition. If they look worn, replace them. They are very cheap and easy to do. If that doesn't do it. Id say you have trash in the carb. It is the factory 2 barrel?

 

Yes it has the original carburetor.Last week I took the top off & cleaned up the gunk in it.I sprayed the inside w/carb cleaner.I also replaced both gaskets.None of this helped.

 

Hmmm, did you blow out the idle circuits with compressed air by chance? It sunds like there is trash in those, but I wuold think you spraying it out should have helped. While its messing up you can take a plastic screwdriver handle and tap on the carb and see if it helps. If there is trash in it that will sometimes jar it loose enough to make it run better. If that doesn't help I would look into the points, although when they wear out it usually doesn't go back and forth.

 

i'd also check for vacuum leaks, although that should just idle it higher a bit. probably your carb has some gunk up in there though.

 

Was it doing the same thing "before" you "cleaned" the carb? If it wasn't then you have managed to mess something inside the carb up. Float, screen filter, accelerator pump etc. If it was doing it before the car cleaning then I suggest you follow an earlier suggestion and make sure the ignition system is firing. Along with points a weak ignition coil can cause firing problems. Check plug wires as well.

 

Probably points, but you can remove the air cleaner top and look down the carb throat with warmed up and it at idle.If you hear a "crackling type noise" when the problem happens you should see fuel coming out of the venturis at idle (it shouldnt) this indicates the float is overflowing and there's crap in the needle valve which allows fuel to overflow into the carb throat.