I have a 72 chevelle malibu and have put a 350 I built in. I have a fairly large cam (294 dur.) and I am having problems with my Vacuum advance. I have the timing set @ 18 deg. btdc and the mechanical advance is operating correctly. When I hook up the vacuum advance the car idles very rough and will die when I put it in gear. I have a Hei distributor and the car runs great without vacuum advance. Do I need to hook it up or should I just do without?

Thanks

Hooking it to ported or manifold vac source? Have you checked to see how much advance the canister is throwing in? Not timing the mill with vac. advance hooked up right?



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'70 SS 396
4spd, 4.10's and a smile
TC# 1341
ACES# 05388
Beaux
The SS (http://www.chevelles.com/showroom/btmyss.JPG)
The Rat (http://www.chevelles.com/showroom/btmill.JPG)- Plans for a 496 in the works.
Interior (http://www.chevelles.com/showroom/midint.JPG)

Life is a gateway drug that leads to Chevelle addiction.

I do not run my vacuum advance.

~18 base and 36 total with mechanical advance.

You can prove your poor running theory by just spinning the distributor more advanced. there is a window that you will "idle high" at. 10* may sound lopey, but throttle response will suck. 25* and your almost at pre-ignition with a very slowly moving rotating assembly. i.e. your partially compression the A/F as it's combusting, too soon. But it's all small details. http://www.chevelles.com/forum/smile.gif

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-Just call me Otis
71' 3880# with me. Big Block 402, Merlin oval heads, 10.2:1CR, TH400, 3.73 posi,
1/8th: 8.0 @ 88mph
BEST 60': 1.85 w/street tires.
BEST 1/4: 12.5 with 1.89 sixty foot (street tires)
BEST MPH: 109mph

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I am timing it with the vac unhooked and am using manifold vacuum. I wonder if the vac can on the distributor is giving it too much advance. It is a 20 inches Hg unit.

I am timing it with the vac unhooked and am using manifold vacuum. I wonder if the vac can on the distributor is giving it too much advance. It is a 20 inches Hg unit.

<BLOCKQUOTE>quote:</font><HR>Originally posted by clem72:
I am timing it with the vac unhooked and am using manifold vacuum. I wonder if the vac can on the distributor is giving it too much advance. It is a 20 inches Hg unit.<HR></BLOCKQUOTE>

Unhook it and see where your initial is. Hok it up and see where your timing jumps to. This should be an indication of how much the canister is throwing in, given it is operating at the correct amount of vac. at idle, and you are seeing full advance of the cannister. The other thing to beware of here is how man Hg's of vac is needed to start bringing in the vac advance. If you have say, 15 Hg's at idle / part throttle and the canister needs 20 Hg's of vac to start operating its useless to you.

I would suggest a Crane adjustable unit if you are going to run vac advance. Adjustable for the amount of vac advance thats added (usually limited to 10-12 deg.) and you can also adjust at what Hg the canister starts to operate.

Not to worry if you dont use it either. Fuel economy and part throttle might suffer a bit but I have ridden in Mikes car, he doesnt run it, and his Velle runs like a champ and gets up like a fat man when the dinner bell rings.

------------------
'70 SS 396
4spd, 4.10's and a smile
TC# 1341
ACES# 05388
Beaux
The SS (http://www.chevelles.com/showroom/btmyss.JPG)
The Rat (http://www.chevelles.com/showroom/btmill.JPG)- Plans for a 496 in the works.
Interior (http://www.chevelles.com/showroom/midint.JPG)

Life is a gateway drug that leads to Chevelle addiction.