I would like to try out a 390 cfm Holley carb that is on hand. It has had a governor removed, and has no ported vacuum source for the dist. So how should I go about setting up the dist. for manifold vacuum? The dist. is a later model centrifugal advance Autolite, with 10 degree weight slots, and a good adjustable vacuum. Vacuum at idle is 18-20 with the 2100 2V. It seems to make sense that the initial timing should be very low, like 0-2 degrees?

Mike

 

You'll probably find that somewhere between 10-14 degrees of initial is what it will like. The distributor is only providing 20. It might actually like more mechanical advance, too.

If you're using a spacer, you can drill and tap it for a nipple. You may be able to use the port in the back of the manifold. Or drill and tap the manifold.

 

10 degrees is a typical initial timing for a dist. with ported vacuum. But if the dist. sees 18-20 on the idle manifold vacuum, wont that give way too much idle advance due to the addition of most if not all of the vacuum advance?

The carb has an outlet for an 1/8 in. hose on the side in the center, which probably will be the attachment point to tap into manifold vacuum. The fitting goes where the plug is in the picture.



Let me throw these numbers out. They may or may not make sense. Assume vacuum advance has been adjusted for a max. of 12, and all 12 is in at 18-20 mmHq (not sure that is the correct unit). Then given an initial advance setting of 4, the idle advance would be 16. Right, Wrong?

Then assume springs have been lightened, and all centrifugal advance is in at 2500. Cruise vacuum would still be quite high, so cruise advance would be 36?

If this is the right thinking, it sounds like a 13 degree dist. weight slot would work a lot better than the 10 degree, in the above example giving a cruise advance of 42.

Just trying to think this thing out before hand.

 

You shouldn't have trouble running 10-14 initial with the vacuum advance getting manifold vacuum. You'll probably have to do some fine tuning but it will be fine. I'm running 14 degrees initial with manifold vacuum to the advance unit.
That port will be the ticket if it provides the manifold signal.

 

Ok. Thanks Charile. I'll give it a try. The intake is due here in 4 or 5 days so it shouldnt be too long. Mike