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Username Post: Vacuum Advance- how is it supposed to work?
wayloud72 
Forum Newbie
Posts: 17
wayloud72
Reg: 04-07-10
04-08-10 09:53 AM - Post#1894942    
    In response to kitabel

Wow, some interesting stuff in here. Here's my thoughts... One comment was made about basically trying to get max advance at idle to try and fire the mix. How much advance do you want at idle? Also a comment was made on exhaust gas dilution. Now if that's an issue, you have so much overlap in the camshaft, that vacuum isn't really much of a worry for what you're doing. The whole idea of the vacuum advance was for mileage and will make the engine run cooler, am I not right? Anytime I set a motor up with whatever distributor I used (HEI, MSD, Stinger, etc.) I dropped it in, unplugged the vacuum and brought the motor up to around 3000 rpm. I use a dial-back timing light so I can set the timing at what I want. I want total mech. timing at 36 degrees to start, and tighten the distributor down (put in lighter springs if it's not in by then). Check the timing at idle and on HEI's it's usually around 18-20 degrees. If you're running a Holley carb, they are pretty much known to run really rich at idle unless you live below sea level! Unless you buy an aftermarket HP or someones other carb body with adjustable air bleeds (need to put smaller ones in, to to make it crisper at idle) Now maybe some people want full advance at idle, but with a small load it could cause detonation (looking at the plugs 'cuz you can't always hear it) but 18-20 initial is more than fine with me. I prefer ported vacuum because it's throttle controlled and I don't want the extra 12 or so degrees advance unless the motor is under NO load and cruising down the freeway. The next thing to do and really make it right is to phase in the distributor so it's not trying to fire the next cylinder. I'll explain how to if anybody wants to know.
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