You can check the mechanical advance with a dialback timing light and a tach, start at tdc, few rpm, dial back to tdc, few more, back, few more, at some point you should be able to graph out the advance vs. rpm curve and the total centrifical advance. If you tell me the Delco Remy number for the distributor, I can sort out what the mechanical advance curve should look like, I.e., when it should start, how much at what rpm, total at what rpm. Then you can compare. If you have access to someone with a Sun or Allen distributor machine, that exercise is much easier and a bunch more accurate.
I just rebuilt a 2403 55-62 235 distributor. Had it on the sun machine for an initial look see and discovered that the mechanical advance was coming in very late and the total was coming in at an rpm that was way too high. The advance on these things is under the breaker plate so you have to take it all apart to see what is going on. Found a broken pin and advance spring, the spring had wedged under one of the weights and rust had accumulated, as well as a thick coating of dirty and heavy grease. Once I rebuilt it and ran it on the Sum Machine, the advance came up to perfect specification. So if your curve is way off, then something else is up and it might need a little more attention.
The first time I had a distributor rebuilt I could not believe the difference in starting and running. So if your distributor is really not close to the specification it’s supposed to be, consider having it rebuilt.
