Denny:You know that the vacuum only works at low RPM's let's say up to 1200 after that the centrifugal advance comes in and takes over at this point you can throw the vacuum advance away. do you have a timing light with the dial on it I'm going to guess that there should be about 24 degrees total advance set the dial to 24 degrees run the engine up to about 1800 and see if the ball lines up with the mark and if it doesn't turn the dial until it does then you will know it not in the dist.You have no vacuum to the dist. at idle because the vacuum port is above the thottle plate as soon as you open the thottle air moving across the port hole starts a vacuum pulling the advance open. And your saying that the only way you can came the engine run is at full thottle if you had a vacuum gauge on a normal running at full thottle the gauge would show zero and as far as the backer fire if the engine leans out weather because the jet pluged or not enough fuel is getting to the carb the cylinder tempature is going to go up high enough to get a piece of carbon glowing and firing the charge when the intake valve opens also even with a fuel pressure gauge you may have pressure but no volume Just a thought.
Paul
