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Holley 1940 Carburetor Flooding, or Too Rich Trouble Shooting:

Flooding, or running too rich is technically two different things, but in both cases too much fuel is getting dumped into the engine. When gas is coming out of the top of the carburetor, or from the throttle shaft end, then that is flooding.
If you are getting black smoke from the tailpipe, or the engine smells gassy, then that is too rich. Also when the spark plugs burn black indicated a too rich situation.

Electrical problems can also cause a too rich situation, but we will concentrate on the carburetor here.

The main jet can cause a too rich situation, otherwise the list below could be the cause of either problem. Look at the spark plugs to see what coler they are burning. Gray is good, white is too lean, black is too rich. When rich reduce the jets 2 sizes and try again. If too lean, then increase the size by 2 and try again.

Check the float for leaks. If you have the black nitrophyl float either replace it, or weigh it to see if it has absorbed any fuel. Weight should be 12 grams. For brass floats - immerse in hot water and look for any bubbles.

Check the float level.

The float pontoon should be level with each other.

Move the float up and down by hand to see if it is binding, or catching.

Any dirt on the bottom of the float bowl could mean dirt got into the needle & seat. Change your fuel filter and clean the gas tank.

Test the fuel pressure, especially if the fuel pump is new. Your motors manual should have the correct pressure, but around 4 lbs would be OK.

Make sure the gasket under the needle & seat was cleaned off totally. Make sure there is only 1 gasket.

Look at the needle to see if there are any lines, or marks on the viton tip. If there is, then it was damaged when installing. Any pressure on the needle while adjusting the float will damage it.

Look for any cracks around the needle & seat inlet - You don't want any fuel to leak around the needle and seat.

Power piston should be free to move up and down easily. If stuck open, the power valve will be open all of the time. allowing too much fuel through.

Check the main discharge. There should be a check ball and a check weight on top of it.

Check weight missing? You can use a 2nd check ball instead.

Check the main discharge to see if fuel is dribbling out while idling. That would indicate a check ball problem.

Watch a video about the 1940 flooding:

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