[Formulajones]

Originally Posted by Shiny

Understand the solenoid part, just wondering if there was something else built into the housing or fittings that "leaked" or otherwise provided vacuum advance at idle or in lower gears?

I suspect not, which means a 70 V8 had ZERO vacuum advance at idle, correct?

The way it worked a couple things had to happen. It ran through a transmission control spark solenoid, and the vacuum was provided by a temp controlled switch on the intake manifold. The carb in 1970 had no provision for ported manifold vacuum.

I'm trying to remember if it provided vacuum at all to the distributor when it was cold, I think it might of to aid with cold start, it's been so long since I disconnected mine. But what I do know is once it was up to operating temp, the only time vacuum would be applied to the vacuum advance on the distributor is when the transmission was in high gear only. So 2 criteria had to be met, operating temp at the manifold vacuum switch, and a switch on the trans that told the solenoid it was in high gear. Both automatics and 4 speeds had this setup.

So to answer some of your question, you are correct in thinking there is no vacuum advance working at idle or low speed (gear 1 and 2) conditions as long as the engine is up to temp. So if you are doing a bunch of stop and go driving the engine is not seeing any vacuum advance at all unless you get up into 3rd gear, or 4th gear with a manual.

It was an emission compliant deal, as it adds vacuum advance hydrocarbons go up is how it was explained to me. California in later years didn't even like the factory setup as I had to have my 70 Formula e-checked and even with the TCS system functioning they wanted the vacuum advance unplugged from the distributor at all times and even stuck a decal on the inner fender stating such. I guess if you got pulled over for one of those random road side checks they were doing at the time. Of course as soon as I left the station I plugged it right back in as the car didn't run as well without it and mileage suffered.

These days I don't use the TCS setup at all and run the vacuum advance straight from manifold vacuum as the car just runs better all around with it in all conditions, idle, traffic, cruise etc....