Vacuum Advance Installation Questions

[Anonymous]

Greetings everyone,
I'm going to replace the vacuum advance unit on my distributor which is located on my 1966 200 block(casting # C6DE6015-B).
I picked up a vacuum advance unit from National Parts Depot here in Ventura. It is a Standard Motor Products, Inc STD VC-42 Diaphram, Vacuum Advance unit.
The question I have is this, the instructions for it say I have to adjust it prior to installation. No problem, its a matter of sticking a 1/8 inch allen wrench in the hole and turning it clockwise to the stop position. The problem is how many counter clockwise turns do I give it after? The instruction sheet shows 50 different distributor tag numbers with different adjustments for each one. Ranging from 1 1/2 turns to 5! I looked all over my distributor for a tag and I can't find one. Any suggestions?

 

[Anonymous]

Dave,

I used to have to replace the vacuum advance a bunch. I never got one that you had to adjust so I can't really help you there. I would say though that I have a good motorcraft vacuum advance that does nto need any "messing with" that I could send you for the price of some postage.

Bill

 

[80broncoman]

I had heard that the older factory units were adjustable. It can be adjusted after it is installed also. All that it is adjusting is the spring preload.
Jim

 

[Anonymous]

Tightening the spring in the advanced causes LESS advance for a given amount of vacuum. Conversely, loosening the spring makes it advance MORE with that same amount of vacuum.

For starters, I would pick the middle ground. If it goes 5 turns, go 2.5 turns first. If it does not ping , loosen it another 1/2 turn and try again. If it does ping, tighten it 1 full turn and try again.

By 'try again', I mean - drive it for several days, listening for ping under your driving conditions.

If you hook this diaphragm up to port vacuum (the most desireable place), the spark advance is maximum when accelerating, up to about 3/4 throttle. Full throttle yields little or no vacuum advance, as does idle vacuum. This is the reason why you want to test-drive it for each setting.

 

[Anonymous]

Thanks for the feedback guys. I'll give it a shot when I get a chance, life has thrown me a curve ball so I'll be unable to wrench for at least a week or two. Nothing to worry about. Nothing broken.