dual quad carter afbs 1964 Riviera

[superwilly50]

I have a 1964 Riviera with the two 4bbl setup. I overhauled carbs 6 or 7 months ago. About two months ago back carb started loading up,creating driveablilty problems. took carb apart could find nothing wrong, but replaced both floats just in case, still loads up badly. It does not always load up. Choke is backed off and I have checked after warming up to make sure choke is wide open. No problem there. When it is flooding/loading up stinks out tailpipes. Whats happening? Any ideas. I have owned this car for thirty years and have always kept in perfect condition.

[NTX5467]

In the venturi clusters for the primary side of the carb, there are ALL of the calibrated air bleeds for the idle and main fuel circuits. These are ALSO calibration points for the fuel mixture curve (i.e., smaller hole = rich, larger hole = leaner). When the idle air bleeds are decreased in size, it'll make that circuit go rich (real quick!). Same with the main circuit.

Several years ago, I had a car with a Carter BBD 2bbl carb. It would not idle once it warmed up (on the idle circuit) and would even die during coastdown for an off ramp on the freeway. I got some thin wire and put it into the idle air bleeds on the venturi cluster. It'd have fuel dripping from the venturi itself when I'd put the wire into the hole! Turned out, the problem was in a reduced diameter "Low Speed Jet" that was in the bottom of the idle tube. Some "twist drill action" cleaned that out really well.

So, make sure the idle air bleeds in the venturi cluster are open and not clogged with deposits. These would be deposits that carb cleaner could not remove, so you'll probably need some very small twist drills from the hobby shop. Go until you just get "metal" from the restricted passage. Might even use some L-shaped bent wire spark plug gap gauges to test the size of the hole first. Wash out the residue of the drill operations and reassemble with the correct gaskets and things should work again.

About 25 years ago, I attended a carb seminar put on by the regional Holley tech rep. One of the "shade tree" methods of idle mixture adjustment, once the speed was basically adjusted, was to use your little fingertip to cover the idle air bleeds on the primary side of the 4bbl carb. When you do this, it makes the circuit for that side go full rich. How the engine speed responds to this added richness is an indication of "rich" or "lean" or "just right". If the idle speed goes up before it goes down from the overrich mixture, the existing adjustment is too lean, for example. If the mixture is "right" there should be no speed increase from the added enrichment. Not quite as scientific as using a tach, but more "hands on" or "analog" in nature.

I hope you saved your old gaskets to match up with the new ones. Sometimes, unseen subtle differences can make a lot of difference.

Just some thoughts,

NTX5467

[carbking]

The problem may be heat and fuel related. Modern fuel is much more volatile than even 10 year ago fuel. Try taking the vehicle out early in the morning to see how it acts. Avoid using ethanol fuel if at all possible.

Jon.