Vacuum/Mechanical Advance Dilemma SB340

Thanks will do! By the way the shop DID re-align the sprockets correctly and the timing now makes sense as measured in the car running! So thats a good thing.

OK great, so we can scratch that off the list at least for now.

Try bumping the initial ignition advance up to 18-20 degrees and see how that helps the idle, just don't drive it obviously because the total advance will be too much. If that makes it better then proceed to re-curve your mechanical advance. Then move on to tuning the carb, first getting the idle mixture and speed dialed in.