Maybe it's the chunks of wood dragging under the car?
:rofl:
Couldn't help myself:rolleyes:
We are assuming it has a standard distributer type ignition system.
It sounds like you are describing pinging, an easy way to check is to set the initial advance to 0 and remove the vacuum advance hose and plug the hose.
If the pinging goes away you have a starting place.
In a side note..
If the vacuum advance was supposed to be tied to a particular port on the carb, but is on the wrong port, you might get too much vacuum at the wrong time.
For instance if it was on manifold vacuum...
(NUMBERS BELOW ARE FOR EXAMPLE ONLY NOT INTENDED TO REPRESENT REAL WORLD NUMBERS, JUST THE WAY THE TWO ADVANCE MECHANISMS INTERACT WITH EACH OTHER )
At idle it would be seeing full vacuum (15 inches) but with low rpm no mechanical advance, so timing would be initial plus full vacuum (10+15 deg = 25 deg) At full throttle the vacume would be lower 5 inches, But rpm would be high so mechanical would be all in and the engine would have maybe initial 10 plus mechanical 25 to 30 deg so 35 to 40 deg advance
At part throttle, vacume would be higher (10 inches) rpm would be higher so some mechanical advance would be in. So perhaps you have initial + vacuum + mechanical 10+ 10 + 20 so 40deg or more.
AGAIN NUMBERS FOR EXAMPLE ONLY