First- this topic has nothing to do with the previous ones.Different car,different time.

O.K.- 454BB,Q-jet carb(rebuilt),Edelbrock performer Rpm intake,points distributor(new points,condensor,weights,springs are medium)
Initial timing set at 4 degrees @ 800rpm

From a dead stop- if you step on the gas hard or just normal the car will almost die.If you ease it on it will accelerate and once up to 40mph or higher the throttle response is good.After checking timing and messing with mixture screws on carb, we finally got the stumble almost out with the timing moved to 10degrees,one mixture screw all the way in and one half way out.While trying different timing settings w/ vacumm advance unplugged, I noticed the mechanical advance was coming in as soon as we started to accelerate.Is this ok or is it part of the problem?I would still like to get some more of the hesitation out that it has when you hit the gas at highway speeds.The vacuum advance is plugged into ported upper slot on the carb, but didn't seem to make any difference either way....

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Joel
T/C#980 1968 SS396 CHEVELLE


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

1. Idle mix needles should be in nearly the same position, and they should be very sensitive to turning them in or out. You may be dealing with a vacuum leak that affects one side of the carb more than the other, a cylinder that isn't running right, or plugged passages in the carb.

2. Mechanical advance should not activate at idle, but will come in "off idle".

3. Better check the accelerator pump again.

Mechanical advance starts to come in at 800rpm.If we set the initial timing at 12 and adjust the mixture screws, we can get around 20gph of vacuum- but the car will die if you stab the throttle and if you ease into the throttle it will have a large stumble at about 1100rpm and then it will pull on through.What would cause the mechanical to kick in so early? It has 2 medium springs in it now.we are thinking we may have a fuel pump problem now causing this.The clear in-line filter just suddenly seemed to not be able to hold any fuel......

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Joel
T/C#980 1968 SS396 CHEVELLE


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

If you rebuilt your carb did you forget about the spring under power piston? This will cause problems you describe.

no extra parts left over.....spring is in.

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Joel
T/C#980 1968 SS396 CHEVELLE


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

Found the problems!!!!!

First- the fuel pump was on it's way out and then finally it died.Also the floats were off a bit and it was flooding a bit.

The engine is rumming good so far, but I have the heaviest advance springs installed and the mechanical is still coming in at about 950 rpm. Is this O.k.?We had to advance the distributor some more cause we were having a stumble at that same Rpm and that was the only we could tune it out.Would a bad vacuum advance cause this?Its plugged into a manifold port currently.

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Joel
T/C#980 1968 SS396 CHEVELLE


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

You don't want centrifugal advance at idle. What is you idle speed?

Add 100 RPM, or so. That's when the centrifugal should start.

If your current 12 degrees initial is WITH the vacuum advance plugged in...You don't have near enough initial advance.

Shurkey- Initial is 12 w/out the advance plugged in.Idle at timing was set at 650rpm and mechanical kicks at 900 or 950.Seems too quick to me but I don't know what causes this.I drove it on the freeway last night for about 20miles and the temp was steady at 210degrees, wich makes me think I need to take some advance out.The stumble is still there off idle, and also if you take your foot off the gas on the freeway and try to get back in it again it will stumble slightly as well.

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Joel
T/C#980 1968 SS396 CHEVELLE


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