Customer Q&A:

Q: No ID on these carbs but I believe they came off an early 60's Pontiac. Dual AFB's on Weiand manifold on a 1957 Chrysler 392 Hemi, probably the 325 hp model.

Engine runs fine but when I recently pulled the plugs they are all black, rich. I was thinking if I could put smaller primaries in that would help the rich mixture.

After reading your info on your website I went out and pulled the metering jet and the primary and secondary jets. The primary jet measures 0.090, the metering rod is about 0.080 in the middle and 0.060 on the end. The secondaries are about 0.070 for what it's worth.

A: Many things could cause it to run rich. Could be that it’s been sitting too long and floats are sticking or needle & seat assemblies aren’t sealing. I would start with a good cleaning and rebuild if you haven’t done so, then consider jetting them down as needed.

If you have already cleaned and rebuilt the carb and the plugs are still black, you’ll want to decrease the jets accordingly. On a transplant carb, it’s trial and error. Get the stamping off the current jet as a starting point and decrease 1-2 sizes at a time until your spark plugs burn medium gray/brown in color.

Q: I rebuild my carburetor and now it’s running rich. What should I check?

A: As with flooding, too much fuel is getting into the float bowl, or extra gas is getting siphoned into the bore because of a plugged air vent.

• Assuming it was running ok before the rebuild, we can rule out the metering rods and main jets.
• Make sure the passages from the idle mixture hole and the off idle above it go all the way through the venturis. The small holes on top of the venturi is what you are looking for. Look at the off idle video to gain some knowledge on how that works.
• If the carburetor was sitting for many months, or years I would highly suspect a plugged passage. Look at every hole you can find and test by blowing air through the hole. Use fine wire or nylon brushed to clear passageways
• Look down the carburetor at idle. Do you see fuel dribbling out of the venturi. If so, the main discharge may be leaking. There will be a check weight in the discharge hole (with pointed end), or perhaps a checkball and a spring above that. Depends on the vintage of the AFB. Take the carburetor off and test the accelerator pump circuit. The small holes on the venturi can get plugged easily.
• It isn't unusual for the venturi gaskets to need to be trimmed a bit so they sit flat. If they don't sit flat fuel will leak into the bore.
• Test the needle & seat. It is possible that while adjusting the floats, pressure was put on the viton tip damaging it. It isn't unusual to get dirt into the needle & seat after rebuilding if the fuel tank and lines haven’t been cleaned.
• Be sure the floats are centered. Move them up and down to feel any catching.

Videos referenced on this page

https://youtu.be/kskxkBvBl9c

https://youtu.be/4mjrnUk0tQI