running rough

[Chevy454]

Sounds like your secondaries are either too big or coming in too fast...if you stab the throttle with the car in park & idling will it fall on it's face?

[SmallHurst]

Falling on its face when you stab it definately sounds like the secondaries are coming on too quick. On the passenger side of the carb back with the secondary is a small screw. Under that screw is a small allen screw that is a set screw. The screw and the spring associated with it control how fast the secondary air dam opens up and how quick the secondary metering rods pull open. Mark where the slot of the screw is at and take your screwdeiver and allen wrench back there and start tweaking this. You will want to tighten this up a small amount, but you do not want to have it so tight that it won't open up. Now comes the fun, finding out if it works properly! When you have it set right, the tires will boil!

[booklearner]

Hi Gtaa:

It sounds like there is too much fuel, does your carb have an adjustable accelerator pump circuit? If it does, try adjusting it so there is not such a strong shot of gas being injected into the carb when you "step on it". Also, just so I am clear, the choke has come off during these tests, correct?

Fooling with the accelerator pump circuit can be tricky, it sometimes takes a bit of experimentation to get it right.

KurtS:

"....Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation...."

I am pretty sure this is wrong. Any car I've ever looked at needed some mainfold vacuum to run (even at WOT). I think that connecting to the mainifold source is an old hot-rodders trick to get snappy bottom end, but it's not the way to set it up for all around good driving IMHO. Not only that, but I suspect it's not a good thing to put 25 inches plus of vacuum on a vacuum advance designed to see only 10 or 15 inches of vacuum (mercury)

-BL

[gtaa9]

At an idle it snaps great no problems,but when I'm driving down the road and nail the throttle it hesitates bad no power at all.Just so you guys know its a 400 4speed.

[booklearner]

Before I suggest anything else, I need to be clear.

Do you mean when at idle and in drive when you step on it, it is snappy, or do you mean when at idle and in park (or neutral) and you step on it, it is snappy?

If you are connected to manifold vacuum this makes sense, manifold vacuum falls off at the throttle is opened, where as ported vacuum will come up as the throttle is opened.

-BL

[Plowman]

I agree 100% with Kurt S. The only thing I saw that was over looked was that the vacuum advance should pull no more than 10 degrees timing. The part number for a points' distributor vacuum advance that does this is #d1308a. It's the hot set up for idle because less gas is used to idle and is not as loaded up in traffic.

[gtaa9]

At an idle with the car in neutral and nail the throttle its snappy.When I drive the car and nail the throttle it hestitates big time.

[gtaa9]

I tried both ways with the vacuum advance(in the back of the carb were main vacuum is and the left front of the carb were the ported vacuum is)there was know change either way.I mentioned this before I noticest two black marks on my garage floor from my tail pipes.Does this mean that the carb is running to rich?