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If you are still running a stock-type fuel pump, I'd suspect the needle valve and float before anything else, as K & B say.
Can you rig up a simple gravity fuel feed to test this? This would consist of:
-- Take top off carb and verify that float bowl is empty.
-- Hook up a length of fuel line to, say, a big funnel that you can hold slightly above the engine. Hook the other end of the fuel line to the carb's fuel inlet.
-- Slowly pour some fuel into the funnel:
-----If the carb just keeps swallowing fuel until it comes out the air intake, the float system is not shutting off the fuel. The problem can't be the pump, because there IS no pump. It could be that the needle valve is stuck open, or that the float has sprung a leak and doesn't float anymore.
-----If the carb stops swallowing fuel as normal, dump the rest of the gas out of the funnel and then take the top off the carb again. Check the level of fuel in the float bowl. If correct, the needle valve and float system is working OK, and you've got to suspect the pump or some other sort of problem.
[Bengt already knows this, but for the benefit of mechanical newcomers who might be reading this: the fuel pump does NOT, as you might think, pump fuel into the engine. All the pump does is keep full a little reservoir of fuel inside the carburetor; this reservoir is called the float bowl. Air rushing through the carburetor sucks fuel out of the float bowl in proportion to how much the engine needs.
To keep the bowl full without overflowing, the carburetor uses a float and needle valve. These work exactly like the float and valve in your toilet tank! If you take the top off the toilet tank and then flush it, you'll see that the water level in the tank drops. This lets the float drop down. The float is on the end of an arm that is connected to a valve, so that when it drops, the valve opens and starts letting water run into the tank. As the water level rises, the float floats on top of it. When the float gets high enough, the valve closes and shuts off the water. What's inside a carb works exactly the same, only smaller and with gasoline instead of water.
What may be happening inside Bengt's carb is that either the valve isn't shutting off when the float gets high enough, or that the float has gotten 'waterlogged' so it doesn't float up as the level rises.
When either of these happens in your toilet, the water goes out an overflow tube and your toilet "runs" all the time -- which is annoying.
When it happens in a carb, the excess fuel flows out the passages into the air intake, letting much too much gasoline into the engine. Depending on how much comes out and where it goes, this can cause the engine to run poorly or not at all, or wash the oil off the cylinder walls and ruin the engine, or catch fire and burn up your car, garage, house, neighborhood, etc. -- which is VERY annoying. This is why Bengt, obviously an intelligent person, keeps a fire extinguisher handy when working on his carb!!!]
posted by 68.13.13...
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