I don't want to hijack this post but all the info here has been great as I have wondered the same things on my car. My question is how to test if your vacuum advance is working. In theory when I am at idle and set my timing at a certain point with the vacuum advance disconnected at lets say 10* and pulling about 15-16 in of vacuum at idle, when I reconnect the advance to the spark port on the side of the carb then shouldn't it jump forward a few degrees? If it doesn't does that mean my vacuum advance canister is bad? Same as if I accelerate the engine with or without it connected it seems like the timing advances at the same exact rate in any part of the rpm range