Remove your distributor cap, grasp your rotor and turn it back and forth. You should have some play but not a lot...it should be firm feeling. That's a good indication of the gears down there. Please also remember you have mechanical advance (although this almost never fails other than if the weights get rusted and won't move or if one of the springs breaks or pops off and then you will have greatly increased timing at low speeds), and retarded timing will cause your engine to run hot...over advanced timing will cause detonation, etc. And it is interesting if you think about it. You could be driving along on a flat road at 40 mph...maybe 2000 rpm and all is Jake. At that point you may have a total spark advance of 28 to 30 degrees (vac + mechanical). Possibly even a bit more. Then you get to a hill and to keep the same speed you hit the gas. This drops your vacuum from maybe 16 down to 3 or 4 and it knocks your overall spark advance down also. If it is a long hill, you could increase your engine's temperature by the time you get to the top...because your spark is happening at the wrong time during this.
Yes, I expect advancing timing would mask a faulty vacuum advance canister. A vacuum leak might be similar but please remember vacuum advance depends on ported vacuum and this depends on air velocity and to a degree air temperature. It is different from manifold vacuum although if either is messed up, your performance will suffer.
Last edited by Jon G; 08/02/2024 4:38 PM. Reason: clarification
