vacuum advance - Off-Road Forums & Discussion Groups
Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

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post #1 of (permalink) Old 12-05-2000, 01:35 PM Thread Starter
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vacuum advance

Ported vs. manifold vacuum to distributor?

What's the idea behind having ported vacuum advance? Its common on later model carbureted cars. I've been running my HEI with manifold vacuum for the last couple of years, based on the theory that under heavy throttle the charge density increases and therefore cannot handle as much advance. Ported vacuum seems to do just the opposite.

I have no idea what sort of switched / combo / complex vacuum setup was originally on my jeep, but I went with manifold vacuum right from the start when I switched to HEI and the added vacuum advance at idle really made it idle stronger. I am wondering if I could get more performance out of my Motorcraft 2100 carb at low throttle opening by making some changes. I know that from checking it with a vacuum gauge, the vacuum drops off significantly when I apply part throttle, so that would reduce the advance significantly by my thinking. I want to optimize this setup, so I am wondering what others have tried.


84 CJ7, 258, HEI, M/C 2100 carb, 5 inch lift, RS9000's, 33x12.5 BFG M/T's, Lockright, full cage & belts, Xenon flares, AMC 20 1pc axles, GM dual diaphragm brake booster
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