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Old 05-31-2010, 04:05 PM
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Opinions, dumb idea: Using vacuum canister + vac advance to avoid hardstart 38'

Quickly: I have a 383 stroker weekend driver with 38' total distributor locked full advance and using an MSD timing computer for 20' retard on start and adjustable idle timing (I can idle anywhere under 38'). Been like this for at least 10 years, maybe 15?? The engine calls for 38' total timing.

No weights, no vac advance used for years.

Even with the MSD computer retarding my start timing 20' (goes down to 18' when the starter is cranking) I still get some hot days where the engine wants to spin in reverse and the starter is crying a little. I have a switch to kill the ignition which works. Usually its after driving, getting gas, and then going to restart the car (all warmed up and hot and gas flowing too well)

Today I tried this setup which appears to work well so I ask opinions:

I have a vacuum canister (for brakes) that holds somewhere around 18hg after I rev the engine. Need that for my brakes with the cam I have. My hg never goes below 10 when I press on the brakes and stays there when I hold the pedal down. At idle the engine wont get below 10hg but cant get higher because of the cam, thats just the average hg at idle give or take. But the brakes hold well and stops fine

I just hooked my vac advance on the dizzy, adjusted to kick in instantly, to the vacuum canister for the brakes. THEN, retarded my timing something like 20' (just a guess). The point is that when I first start the car I am NOT locked at 38', my distributor is probably locked at 18' now because I turned it back. After about 2 seconds as the vacuum canister fills (empties, you get the point), the vac advance kicks in at 5hg, raises my total timing back to 38' (which I checked to confirm). The timing holds because my vac advance never releases.

I ran the car around and never stumbled because the vacuum canister always had well over 10hg...enough to hold the vac advance canister in total advance. And, at WOT where I have no vacuum, it doesnt matter because the vac is coming from the canister which is still holding enough to pull the vacuum advance in.

Long winded but I wanted to cover the story. My idea is when I start the car I have maybe 18' on the distributor because its locked, the MSD timing computer throws in additional retarding for a better start, and then the vacuum advance pulls in once the car is started to get me back to 38' total locked timing. The MSD computer is still dropping my idle timing down and doing what it should.

YES, I know ideally I should have weights and vac advance canister hooked up. But aside from fuel economy, does anyone see this as a really dumb idea? Its nothing different than any other radical cam riding at total timing locked out except that my total locked out timing isnt in effect until the car runs.
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