dusterguy225,
If you don’t have a dial-back timing light mark 10 degree increments with white-out starting from the factory timing mark. As your timing advances you will be able to see & easily estimate 2 1/4 degree increments between your white marks.
What DI & Agg Ted are looking for is a list of rpm points and timing advance reading at each of the rpm points, and if you have a vacuum gage reading manifold vacuum at the same time that information can be added to the list also. I did this very drill a few months ago when recurving my distributor, and discovered a lot of interesting trends. You will need a tachometer for this project.
Get out a clip board, pull on your white lab coat, stock your pocket protector with colored pencils, warm up your engine, and establish a timing base line. I have several loose leaf notebooks holding every start point & change I have made to my car sectioned off by engine, transmission, suspension, electrical etc. This information, when organized this way, is handy to have at your finger tips, saving a lot of duplication of effort.
Start at Idle in “N†with vacuum advance vacuum line disconnected from the carburetor & its carburetor port plugged off; record rpm, degrees of advance, and vacuum inches HG for this, and for each 100 rpm increments, until the timing dose not advance any higher. Just turn the idle adjustment screw on the throttle in to raise the rpm. You now have established your mechanical advance curve. Back off the idle screw to bring engine to curb idle.
Second step:
Connect the vacuum advance canister to carburetor, and repeat the 100 rpm data recording points until timing dose not advance any more, and back off the screw to reset curb idle. Now you can see how the vacuum advance interacts with the mechanical advance. You will be able to see when the vacuum advance kicks in, and how it adds to the mechanical advance to give a much higher total advance.
You may recall as the throttle is opened under acceleration the manifold vacuum drops, at WOT it goes to zero. The vacuum advance reads these changing vacuum levels and automatically retards timing under acceleration, and advances it when throttle is held steady or constant as when cruising on flat ground or down hill. When timing is advanced to its highest level that is when you are getting maximum fuel economy. Engines don’t like a lot of timing under acceleration, if too much advance is present, the engine will ping indicating poor burning dynamics in the combustion chamber.
Just list all the data points here, and we will be able to see if all is well, or not.
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When looking at it with a timing light, its really jumpy so its kinda hard to tell anyways