Bullit:

The timing seems about right. Sorry you had to go through all that to find out, but it had to be done.

You're sure you can't lean the idle out with the mixture screws, right? First, check that again. Just as a test, screw them in until the engine starts to stumble, then back them out ONLY until it smooths out, and no more. This isn't the preferred way to set the idle mixture, but it will determine if perhaps the idle mixture screws can fix the problem. If it can, we can work on that. If not, we know to look elsewhere.

Next, go back to post 8 or 9. CKJ440 posted a good picture of where the throttle plates are supposed to be in relation to the transfer slots at idle. Pull the carb, be sure the choke is all the way off (so the fast idle is not set) and be sure the throttle plates only leave enough of the transfer slots exposed so that what you see looks like a square. If it looks like a rectangle, that could be part of the problem. Check the secondaries for the same problem. This is usually a problem on larger/more radically cammed engines, but like the timing, the basics must be covered first.

How old is this carb? Is it fairly new, or has it been sitting around for a long time? Is it time for a rebuild?

Is the carb clean? Spray some carb cleaner down all 4 idle air bleeds. If they're blocked it can cause a rich idle. If you don't know where they are, and if no one else comes to the rescue with a good picture (hint hint), I'll find one and post it tomorrow.

Jim