Engine Timming

[Nitrate]

1981. 2000. Do you disconnect and plug the vacuum line to the distributor when setting the timing? RB

[76was124]

Yes

[Nitrate]

I know that that's common practice. Odd that I don't see it mentioned in the owners manual or the aftermarket Brooklands work manual, which, by the way, has the drain and fill plugs for the manual and automatic transmissions reversed in their photo pg.40. RB

[wizard124]

I know that that's common practice. Odd that I don't see it mentioned in the owners manual or the aftermarket Brooklands work manual, which, by the way, has the drain and fill plugs for the manual and automatic transmissions reversed in their photo pg.40. RB

My vote is no

[RRoller123]

Since it is timed at normal idle speed there is no reason to disconnect the vacuum line. (I am assuming you are talking about ignition timing with a timing light). Put the light on and time it with the line connected.

[76was124]

Hmm.....I'm outvoted, so maybe I am wrong? I thought the advance worked off the manifold, so even at idle, with no load and at lean idle, some vacuum is created.

I guess an easy test is to disconnect the vacuum line at the advance, plug the line and see if the idle changes.

[Nitrate]

1981.2000. Since I see no mention of disconnecting the vacuum I'm going to time it with the vacuum connected. Vacuum is highest at idle. The mechanical advance weights are not active until higher engine speed. Can someone give me a definitive yes or no on disconnecting the vacuum line? RB

[donm]

Funny, I just went through this this morning. I had to replace my vacuum module and when I set the timing I removed and plugged the line because when it was connected it cause the timing to advance a bit.

BTW, just why are there two advance systems, centrifugal and vacuum? Seems kind of redundant, no?

Lately I had been running without the manifold heat shield and now I'm wondering if the heat destroyed the membrane in the capsule, which I assume is rubber. Just in case, I put the heat shield back in place.

[bobplyler]

Two systems because they work differently. Centrifugal works on engine speed alone. Vacuum works via engine load.

[76was124]

To add a little bit more to Bob's reply.

Vacuum advance works during acceleration or when going up hill at constant speeds.

[Nitrate]

No vacuum is highest at idle and when cruising at highway speed. When throttle plates open during acceleration going up a hill the vacuum decreases, that's when the centrifical weights take over. That's why there are two systems. RB

[bobplyler]

It would be, if vacuum for the distributor is taken from the manifold. It isn't. It's taken from the place in the carb that operates vacuum secondaries. It's higher vacuum when more air is flowing.

[Nitrate]

Your confusing the fuel system with the ignition/ advance /retard system that is regulated by engine vacuum and the mechanical advance weight in the distributor. You are correct in saying that a ported vacuum take off point results in no timing advance at idle. But once the throttle plates are cracked just a hair it's just like manifold vacuum. It decreases when you open the throttle going up hill and increases when you are in cruise mode. RB

[gandyrail]

Brads books says to take off the vac line.

[Nitrate]

Gandyrail, Thanks very much for letting me know that. I have Brads book but missed that refrence. RB