Electronic distributor with no vacuum advance?

[ebrown0104]

Is it possible to have an electronic distributor without a vacuum advance? My new (to me) 1977 has been converted to a newer style electronic ignition, but there's no vacuum advance on the distributor itself. I was looking around and I don't see anywhere to even bolt one on to the bottom, and also the pickup is bolted solid. I'm assuming that the complete distributor was changed out and didn't just have the newer guts installed into the points-style one, but it could have been done that way. Thanks for any help.

[fiatfactory]

.

[ebrown0104]

Thanks! I have a 1978 Honda CB750 with dual points and I've never had an issue with them - just set the gap, get it timed, and it runs great. Of course, there's two sets of points, two coils, and 4 plug wires. It's a simple setup, no switching relay or anything overcomplicated.

Is there any advantage to a vacuum advance setup over the non-vacuum that I have now?

[131]

Better cruise economy apparently, I've never had it on any of my Fiats, and I don't yearn for it. Going from electronic ignition back to points would be a retrograde step IMHO.

[bradartigue]

You have a Marelliplex. It is a piece of gold.

The Marelliplex distributor was sold along with the coil pack as a replacement through FIAT dealers (and eventually, parts vendors). It is exactly as you describe, an electronic distributor without the vacuum advance. They are very expensive if you can find them now-a-days. They are very nice indeed, congratulations!

In the 1990s I paid more for Plex kits than I did for some of the cars I had...

[baltobernie]

As engine RPM increases, it is necessary to "light the fires" earlier to ensure complete combustion. With a mechanical distributor, this is accomplished by a centrifugal advance mechanism. Vacuum advance is used in conjunction with centrifugal advance to provide an additional "head start" to the combustion process at idle and under light load conditions, which are typically on the lean side. Without an electronic distributor to perform calculations beyond basic engine RPM data, vacuum advance is very helpful in delivering good driveability. Vacuum advance disappears quickly above idle and part throttle, and has no effect on total power. Of course, in modern engines all of the decisions regarding spark timing and fuel delivery are the responsibility of the computer, which adjusts both of these (and valve timing in many engines) for each revolution of the engine.

[fiatfactory]

.

[ebrown0104]

Oh I definitely don't plan on going back to points. If my car had points it probably wouldn't be the first thing I'd change, but I'm not turning back.

I did notice that the ignition module has a GM brand on it...