Quote:

---

The answer is simple, you have a bad cylinder. Your mechanic told you. One man's "rock or shake" is another man's vibration.

If you remember which hole was bad, pull the spark plug wire on it and see if it makes any difference in the engine's behavior. I bet it gets slightly worse, but doesn't change a lot.

Whatever you do, don't go making a lot of changes all at once. This is a simple problem with an expensive solution. You probably need a different engine or at least a valve job on your existing heads.
If it is a valve, you can sometimes tell by pulling the coil wire and turning the engine. Listen for a hiss every other revolution. If it comes through the carb it's an intake valve. But dollars to doughnuts it's an exhaust valve and the hiss will be heard at the exhaust.

If this is the case, I'd suggest looking for a mid-80s Fifth Avenue for heads or complete 318.

Also, unless your 273 came with a factory four-barrel carb there's no reason to put in 91 octane fuel.

Keep us posted. There's more collective brainpower on this board than in most garages.

R.

---