AFB AVS Troubleshooting

My AFB has a dashpot. Is it necessary?

Yes, it works with the automatic transmission. Not good for the engine to run without the dashpot. Too much unburned fuel when stopping.

Gas is dripping from the venturi after shutting down

  • Main discharge may be leaking. Remove the venturi and with fuel in the float bowl hold down the check weight and/or check ball and pump the accelerator. If gas comes out of the hole where the weight is placed you have a leak. Tap the weight lightly to form a better seal.
  • The fuel pump pressure may be too high. Test for approximately 4.5 lbs.
  • Make sure the gas cap is vented. Non vented will form a vacuum in the tank and gas will be siphoned.
  • Percolation is possible if the engine runs hot.
  • Be sure the fuel bowl vent isn’t plugged off, or somehow kinked. The fuel bowl must be vented, or gas will be siphoned.

Carter AFB Flooding

There are many reasons your carburetor is flooding. Flooding means fuel is overflowing over the top of the carburetor. Running rich means the exhaust has black smoke, or there is a strong smell of gas.

  • Test your fuel pump. New fuel pumps are especially troublesome. Check your motors manual for the proper pressure, but for the AFB it should be around 4.5- 5 lbs. Too much pressure will cause the needle not to shut off the gas.
  • The needle & seat may be damaged. If while adjusting the float, pressure was put on the needle then it could easily have damaged the viton tip. If the needle is new, wipe the viton tip with mineral spirits to wipe off the black residue. Turn the top upside down and while the floats have the needles closed, blow into the fuel inlet (not too hard). Air should not get through.
  • Make sure there is a gasket under the seat and there is only 1 gasket. We have seen old gaskets left behind, then a new one added on.
  • Test your floats for leaks. Heat up some water and immerse the float. Bubbles would indicate a bad float.
  • Check the float level.
  • Your floats should be centered in the float bowls.
  • Make sure there is clearance on each side of the float tangs.
  • Move the float up and down to feel for any resistance, or catching.
Adjusting AFB Float
  • There may be dirt getting into the needle & seat holding the needle open. Filters may be dirty, or perhaps the fuel tank is dirty.

Flooding can be summed up with one idea. Too much fuel is getting into the float bowl.

Starts Hard in the Morning

  • Before starting look down the carburetor and pump the gas once.
    • You should notice 2 things. The choke valve closes & gas squirts out of the main discharge.
    • If the choke valve doesn’t close then check for a bad thermostat, or perhaps there is a linkage problem.
    • When no gas squirts out then the bowl is empty, or the accelerator pump circuit is clogged.
    • The bowl might be empty because it’s leaking out of the bottom somewhere, or the gas was siphoned out after turning the engine off.
    • After running the engine (operating temp), turn the engine off and look down at the discharge. There should be no gas dribbling out.
    • After running the engine (operating temp) and at idle look down the carburetor to see if gas is dribbling out. If it is then the check weight may be leaking.
    • No gas squirting out might indicate a clogged pump to discharge channel.
    • Make sure you have a vented gas cap.

Pops Through Carburetor, Idles Rough

While the ignition could be the problem we will only address the carburetor here.

This condition is most likely a lean condition. Here is a list of possible culprits:

  • Float level, or float drop not allowing the float bowl to fill up.
  • Weak fuel pump pressure. 4-5 lbs.
  • Most AFB’s use a clip to connect the needle to the float. This way when the float drops the clip helps pull the needle out of the seat. A missing clip might mean the needle is sticking closed.
  • Floats catching because of a worn float pin.
  • Needle damaged from too much pressure put on the viton tip.
  • Engine sat for months causing the gas to turn and coating the inside of the carburetor with varnish.
  • A vacuum leak may be letting in too much air.
Carter AFB Carburetor Kits
AFB Carburetor Kits
Free Electronic Manuals


Updated on 04/24/2022

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