Okay Gents, a little clarification is in order here.Fiirst off, initial timing is always set at slow, hot idle - NOT at 1200 tpm. This is necessary so that the centrifugal advance weights under the breaker plate in your distributor do not begin to come out and add additional advance. If you set your timing at speeds above slow idle, you are likely getting some centrifugal timing in the mix, which will affect the reading of your timing lighr.
Timing on our flatties is important but not real critical. You want as much advance - turn the distributor counter clockwise to adance - as the engine will tolerate without preignition. Usually this boils down to four to six degrees before top dead center. Too much advance, and you get pinging. Too little advance, and the engine runs hotter, burns more fuewl and has less power.
As to identifying your acceleragor pump. you really must find a shop manual to know this stuff. It shows a break-down of each part and each circuit. Our Caarter carbs are quite simple and easy to work on, but they must be right to work as they should.
I won't attempt to explain the entire carburetor, except to say that at idle, the engine uses the circuit that you adjust with the small screw on the lower side that has a spring behind the head. At higher speeds, the idle circuit is no longer working and the main metering circuit is used. This includes the main jet in the bottom of the fuel bowl and the vengturi cluster in the carb throat.
When you accelerate from idle to higher speeds, a hesitation will take place between these two circuits. The accelerator pumop is just a squirter that richens the mixture momentarly on acceleration. Nothig more, nothing less.
Terrell Macchine rebuilds old vacuum advances. Bernbaum and Roberts also carry these new. Either way, they are spendy - like $65 to 75 a pop.
Good Luck