340 slight dieseling when hot and hard start

67Dart273 said
Where is the timing and what do you have for a timing curve?

How hot does the engine run and "don't tell me" the middle of the factory gauge

Vapor lock is always a problem with this "new world order" fuel. Best thing I did for the 67 before I went with EFI was to

Install a rear mount electric pump

pay attention to tube routing

Install a vapor return system using Wix 33040 / 33041 fuel filter

add a carb base insulator

You might consider blocking the exhaust crossover

and CHECK that the exhaust butterfly if you still have one is opening

All GRATE ideas!!!

Here is a couple more.
Get a quart of water, (atf fluid if your in a area were you can get away with it. aka makes a LOT of Smoke) start eng,remove air cleaner, rev eng to around 3000 rpm. Now, vary slowly, dribble the liquid of your choice into the carbs primary barrels. do not let the eng slow down as you do this.

If its running on, become of carbon build up on the piston. It won't after your done!;)