Author Topic: Distributor Vacuum Advance  (Read 125 times)

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Offline surfguitar58

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Distributor Vacuum Advance
« on: Wednesday,January 03, 2018, 03:50:12 PM »
The DPO (which in this case means “deceased previous owner”, because we don’t speak ill of the dead… yet) of my TCS took Chapman’s “simplify” ethos to an extreme, having removed all Fed emissions equipment (cross-pipes, charcoal canister, vapor tank, etc.) and brake boosters, among other things.

One missing item is the vacuum line to the distributor. I didn’t even notice it was missing until I had been driving the car for a while, and I thought the car was running great! (Admittedly I have nothing to compare it to, this being my first experience with a Lotus twin cam.)

I would have thought not having vacuum advance would be a big deal for optimum performance. Is omitting the distributor vacuum line commonly done? Where does the distributor vacuum line usually connect on a twin cam? There is a plugged port on the back end of my Stromberg manifold that I assumed used to go to the brake boosters. Does it go there?

Complicating matters further, the DPO bought, but never installed a brand new Pertronix Flamethrower electronic ignition distributor, coil and plug wires that came with the car. The distributor has a plugged hole that looks like it supposed to accept a vacuum advance diaphragm assembly (not included with the Pertronix kit.) The installation instructions basically say you can use vacuum advance or not. Dealer’s choice.

So, to vac or not to vac? And, if so, where was the factory connection? Also, is vac advance recommended for electronic ignition?

"A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away."
Antoine de Saint-Exupery

Offline 2483R

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Re: Distributor Vacuum Advance
« Reply #1 on: Wednesday,January 03, 2018, 06:52:57 PM »
Actually, the emissions TC distributor was vacuum retard, not advance. Yes, most just disconnect the hose, the car runs much better without it connected. Set static or idle advance at 10 degrees, and the advance curve will be set by the centrifugal advance.

A good reference is Wilkins, "The Twin Cam Engine" He has advance curves for all models of TCs. The federal emissions advance curve is awful, I don't how the stock federal Europas ever ran.

The brake booster hose did connect to the manifold. But my memory is a little fuzzy as to where the distributor hose was connected (I disconnected mine some 35 years ago).

If you have a Pertronix distributor you are ahead of the game, as the Lucas distributor can be problematic. If the advance curve on the Pertronix can be adjusted, I would try for the European Stromberg advance curve, you can find it Wilkin's book. If you can get the European Stromberg advance curve with using a vacuum mechanism, that is the way to go.

Offline jbcollier

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Re: Distributor Vacuum Advance
« Reply #2 on: Wednesday,January 03, 2018, 07:02:45 PM »
The Strombergs had a manifold vacuum port at the bottom which was used for the vacuum retard canister. Don't hook it up.

Offline Roger

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Re: Distributor Vacuum Advance
« Reply #3 on: Thursday,January 04, 2018, 08:37:45 AM »
The Strombergs had a manifold vacuum port at the bottom which was used for the vacuum retard canister. Don't hook it up.

Dead right. Plug it though or you'll run a bit lean.