Just purchased a '68 falcon and have a 289 in it w/56K on it. Runs great but every so often it is a little tough to start (after it has been running for a while) and when it does it blows a cloud of white/gray smoke out the pipe. I am assuming that this is a carburator problem but don't know much about carbs so I thought I would throw the question out here.
Any insight appreciated.
Also, what should the gap on the spark plugs be?

 

Wow-

My Grandma's 61 (I fix and drive) only blew white when I put Tranny fluid in the cylinders. (Long story helped the engine.) White smoke is some sort of oil or water in your ignition cycle, serious problem. Run a compression test. I am pretty sure you have holes all over some cylinders. Steam is also white... but I think you have oil leaking. You say smoke, that sounds different from steam. Your water jacket may be leaking though! Do not run it until you resolve the compression, if you have good equal compression you're fine but look at the carb. if not running the engine may mean replacing your:

Radiator (overpressurization rupture)
Water pump (overpressurization stress)
The engine itself (oil burning and messing it up)

By then you've got little left. You'd basically buy another 289.

I know I really sound happy happy joy joy about this, but consider. I just bought a 66 Fairlane. See fairlane sat for 25 years need info. That's me. So don't feel bad, you at least know what your problem is, if not how to fix it. I have no idea where I'm at.

As long as it's running you can get worse, so be careful. As long as it's running it's easier to tell what's wrong, so that's a plus.

Best case scenario it's condensation in your carb creating steam. This is so unlikely I am surprised I even put it here but it is possible if you're near a swamp or something.

Good luck, get your compression test and if it's good you're in good shape as the problem won't be near so big.