i understand that initial mechanical timing is important because it needs to be retarded enough to allow the engine to turn over but advanced enough to start.

i also understand that mechanical advance increases as RPM's increase.

i understand that the vacuum advance hose needs to be disconnected and plugged to time ignition at idle. (no vacuum advance). after timing, the vacuum hose is re-connected.

now where i'm confused is the vacuum advance dials in advance under high vacuum states (idle and mid throttle).
this means less advance at wide open throttle. makes sense so far.

where i'm confused is if i start my car, and do not touch the gas pedal, won't the engine get high vacuum turning over the engine and kick back the starter?

ah but here is the other thing.

the centifugal portion of the dizzy doesnt kick in until ~1000 RPM or so ( a little less). At idle total advance = initial advance = ~7.5 BTDC

right, so when I turn over the car the mechanical advance is minimal but vacuum advance is getting full vacuum, right?

wouldn't that be too much to turn over?

what am i missing? I need to understand this. =-)

The port for the vacuum advance is usually placed such that you do not see full vacuum until the throttle plate is open slightly. Plugging it when setting the timing is just a precaution since you will not normally see full vacuum when the throttle is fully closed.



Andrew

OK

Here we go...
7.5 initial advance
15 vac advance (or so)

15+7.5=22.5 degrees AT idle.

But what the key here is how much CAN the engine be advanced to run well at idle? Retard comes in with open throttle, as vac advance cuts down.

I think you're on the right track to figuring out why it ended up being disconnected at the factory after 74.

Personally, I never HAD the advance side connected, but the retard side rubber diaphragm was always toast. The advance side was very responsive and tight, which also led to my believe and supporting the advance side unhooked therory.

After thinking of my total advance, I was basically running a 009 anyway, so I just bought a 009. 32 degrees is enough for me.

b

The vacuum advance pick-up hole is above the throttle plate. There is NO vacuum advance till the throttle is opened.

Ken

Ken is correct. The vacuum advance port will only be pulling a vacuum when the throttle valve is open a very small amount. So the vacc advance is not active at idle in any way shape or form--in fact, the vacuum retard is active at idle, because it gets its vacuum from below the throttle plate.

--DD

For a more indepth explanation done by Lapuwali see my MJLJ thread and my advance quesitons.

http://www.914world.com/bbs2/index.php?show...mp;#entry750441




Missin ya, James