Here's what I've done....I rebuilt my Quadrajet carb,replaced intake gaskets,and installed a GM HEI and MSD6Al box.I set initial timing at 10 degrees,and it is steady,not fluctuating.Plugs and wires are new and the firing order is correct on the cap.

On the carb, the float height is set at 3/16 from the top as per manual and rebuild kit states.Mixture screws turned out 2 1/2 turns.

O.K.- start up the car,unplug vacuum advance and connect vacuum guage to manifold port and my reading is only 6-8gph and erratic.First thought was vacuum leak at manifold so I spent almost a whole day spraying down with carb cleaner and tightening here and there.No change in vacuum readings.If I put my hand over the carb top the idle doesn't seem to move either.Besides, I would think with such a low reading I would hear a leak this big with a stock 396 engine and exhaust.

So from there I searched the forums for hours last night about ported/manifold/ignition advance/timing etc.
I've altered the timing from 8-12 and still same reading.My mechanical is kicking in at about 1900rpm with the advance kit and two medium springs installed.The only thing I've run across that I think is the problem, lies in the manifold.I ran across a post regarding the carb warming ports in the front of the manifold and the need to close them off with a metal gasket under the base gasket.Not only did I use a base gasket with the holes and trough cut out for this, I also cleaned out the ports in the manifold while I had it off.They were really carboned up when I took it off and I dont think the gasket had the cutouts.Also, the carb mixture screws have little effect on anything and fuel is not dripping, but spurting out the tops of both venturies.I assume to counter the extra pull from the manifold.Also the paint is beginning to burn off the manifold on both sides where the carb mounts.What do you guys think??Would this give me vacuum trouble/carb adjust trouble like this?


Right now timing is set at 10 @800rpm-steady
vacuum advance on manifold(carb base)port,
advance kit has both medium springs installed and kicking in at 1800rpm
I've got MSD instruction book and don't see anything about a Dial-back timing light problem but read it in some topics here.What problem is there?

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Joel
T/C#980 1968 SS396 CHEVELLE


If at first you don't succeed, skydiving is not for you.....

I'm confused.

Is your timing at 10 WITH THE ADVANCE CONNECTED TO MANIFOLD VACUUM?

If it is, that's your problem. NOT ENOUGH ADVANCE.

Try 6-8 with vacuum advance disconnected. Connect vac advance to a TIMED port

I'd expect the mechanical advance to start around 1000-1200 rpm, not 1800. That's too high. Again, not enough advance. Should be ALL IN by 3000 or so.

There is one other factor you touched on. 1969 and older big block (stock, iron) manifolds MUST have a metal shield under the carb to prevent exhaust gas from the manifold crossover leaking into the intake. I made that mistake twenty years ago, and the car ran like crap until I re-installed the stainless shield. In extreme conditions, you could damage the carb from exposure to the hot exhaust gas.

Sorry if I wasn't clear Schurkey- the vacuum advance is not plugged in currently while i'm trying to find the problem.Is the manifold crossover pulling vacuum and causing the venturies to flow gas out of them?Do you know where I can get another metal shield?The auto stores around here don't seem to know what I'm talking about and say they haven't seen that before.Can I just plug them up with some kind of sealer and maybe double stack the gaskets?Or does someone know where I can get one from?

Also I'm going to switch advance spring to 1 medium and 1 light and see where it comes in at.

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Joel
T/C#980 1968 SS396 CHEVELLE


If at first you don't succeed, skydiving is not for you.....