Quote:
BH wrote:
What I do know from practical experience is that a leaky vac advance diaphragm is often overlooked, and the engine is tuned around that problem, at idle. However, when you give it some throttle, the engine stumbles. Perhaps this is due to a combination of a lack of timing advance and a leaner air/fuel mixture - both due to a vacuum leak in the vac advance diaphragm.
Practical experience is about all that seems to work with old-time breaker-point-rotor- distributor ignition systems.
The condition that Big Kev described--black smoke and bogging on initial acceleration or low speed acceleration--is sometimes caused by not enough
initial timing advance. An actual vacuum leak would probably be noticeable by a rough, lean idle condition.
If the vacuum advance itself is not working correctly, I believe it would most likely affect gas mileage and high-speed performance.
A good, easy test is to advance initial spark timing a bit and see if that helps clear up the smoke and bogging/roughness.
Also, is the heat riser working and pulling the choke off properly?
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