I'd check the plugs for soot (as above) to find out which cylinders are running rich. Have you refilled the car lately? Sometimes dodgy fuel will do exactly what you describe..

Alpha I think the problem you mention is something similar to what I had. First do you have an electronic dizzy?

If not replace the condenser & points in the old mechanical distributor.

There both very cheap. Have you changed your coil? The coils are known to pay up after the car has warmed up.

Just a thought.

Alright Gav, I'll check that too tomorrow...

Mmmm... now I need to find out all about Dizzies!

I take it I can buy new parts (coil, condensor, points) at a regular auto shop?

If everything else mentioned is o.k. check your float level.

Its not a problem to buy them at your local autor parts shop, and installing them is pretty damn easy, however, there are usually lots of little plastic spacers/washers, if you don't get them in the right place, and they earth, your car will never start. Just take it easy and pay attention to what goes where, the condenser is also a possibility, when they heat up, they tend to not work well absorbing the extra spark and your car farts and pops when you rev it.

Wasn't the points or the condenser... I'm thinking float level!

Hold on, you haven't pulled the plugs yet!!!!!

plugs are black and sooty, yea, running rich alright.

Good, Now I can sleep tonight.