2.0 Dizzy Question, Maybe I am just an Idiot Options

[Mblizzard]

Ok 73 2.0 built to a 2056. Currently running points. Checked dwell and set to specs. I was setting the timing and I have a timing light that you can set in the advance.

1st question: Can you use the advance setting on the timing light instead of the 27 at 3500 rpm?

2nd question: My dizzy has 2 vacuum ports. One is advance and one is retard. My throttel body only has one vacumm port for the dizzy. Do I need both hooked up?

3rd Question: Do I have the vacuum line on the correct (advance) side?



4th Question: when I check the timing (just for fun) with the vacuum hose hooked up as shown the timing is not anywhere close to 27 at any rpm. That seems odd.

[Cap'n Krusty]

Time for me to check in. The diameter of the retard port on the TB and the one on the vacuum can are larger than the advance port and advance connection on the vac can. That in itself should make it clear which line goes where. With the throttle plate closed, there is significant vacuum on the retard port. If there's an advance port, there will be NO vacuum present at the smaller (advance) port on the TB with the throttle plate fully closed. If the hoses are connected properly (how can they NOT be, given the difference in port AND hose sizes?), the idle speed will be pulled down with the throttle plate closed, and it will rise significantly as the throttle is opened (as retard vacuum goes away). As the advance port vacuum gets stronger, the advance side of the can moves the plate and cause the timing to advance. There are NO variables here other than the strength of the vacuum signal and the freedom of the plate to move. None. It doesn't matter whether or not you unplug the retard hose when setting the timing at full advance, because it has no vacuum once the throttle is opened. Good habit to do so, though. As 914 TBs have no throttle stop adjustment for closed throttle, the plate should always be fully closed when at rest. If the cable is too tight, or the closed position has been artificially altered, that needs to be addressed. If the retard hose is attached to the advance port on the can, the idle speed will be way too high and the timing advance will only reflect the operation of the mechanical advance mechanism. Any questions?

The Cap'n