Distributor Identification and Specs

[webco]

I know there have been loads of posts about distributors but I'm trying to understand the difference between these:
021 905 205 A-B (0231176048)
022 905 205 AA (0231181009)
I've searched the posts but haven't found the info I need.
I believe the A-B is from a '74 California 1.8 and the AA is the '74 1.8 49 state version. What is the difference? I need a distributor for my 2056 with 40 Dells and a mild, streetable cam. Any insight appreciated.
Thanks
Bill

[Dave at Pelican Parts]

According to the factory workshop manual, the only difference between those two is that the AB has both vacuum advance and retard, and the AA only has vacuum advance. The vacuum advance curve is also slightly different. All of the mechanical advance should be identical between the two.

Use either one. You're unlikely to be hooking up the vacuum to a set of carbs anyway, so it shouldn't matter which one you use.

--DD

[webco]

Thanks Dave. I was planning on using the ported vacuum on the DRLA 40's I have. Is that not a good idea?
Thx
Bill

[Dave at Pelican Parts]

Most people don't bother. Using vacuum from one throat gives you a wildly varying signal, and very view are willing to 'T' everything together to smooth it out. Or to figure out if some volume of air is necessary to act as a damper to the signal.

--DD

[webco]

Dave - My plan was to use an anti-pulse valve. Anyone have any experience with using one? I only have one ported vacuum pick up on one of the carbs. I've read that ported vacuum is what should be used.
Thanks
Bill

[Dave at Pelican Parts]

Ported vacuum may work for advancing the timing. The vacuum there should be nothing except when the throttle is open very very slightly, when it will be relatively strong. This can help a little bit with off-idle response if it is connected to the advance port. If connected to the retard port, it will probably be counterproductive.

Try it without--like I said, most people don't bother with it.

--DD