Cleaning a carburetor

This is the carburetor from the Vespa ET2 that I just purchased. The purpose of the carburetor is to vaporize gasoline and combine it with air to be ignited by the spark plug down in the engine.

Here I have removed the the float bowl cover. The tan plastic ring is the float. It controls the amount of gas available to be vaporized at one time. Should the float fail, the carburetor can fill with gas and the gas will not ignite properly. 

Visible inside the ring are two slotted tubes. Those are the jets. 

I removed the float assembly by pulling the small hinge pin. The small pointed obejct is a rubber tipped needle that fits into the tube that feeds gas into the carb. When the bowl is empty and the float falls, the needle is pulled free and gasoline can flow into the bowl. When the gas in the bowl causes the float to rise, the needle returns to its place and cuts off the flow of gas into the bowl. 

These are the jets. They are the passages through which the gas flows and is vaporized. The size of the jet determines the volume of the gas entering the main chamber to be mixed with the air.

The smaller one is the idle jet which provides gas at a stop and at low speed. The larger one is the main jet which provides gas when the engine is revved and the clutch is engaged. The main jet flow is controlled by a needle that is connected by a cable to the throttle handle. When the throttle is turned, the needled is unseated and that allows fuel to pass through the jet and into the mixture chamber.

When gasoline sits for a long time it will evaporate and leave behind a gummy residue. When this happens, these jets can become clogged and the flow of fuel is restricted which affects the air/ fuel mixture and can cause poor engine performance and if not corrected, severe damage to the engine.

I have now removed the idle screw. This adjusts the volume of air taken in by the carburetor. 

The flathead screw above the large opening is the air/fuel mixture adjustment screw. This is the fine adjust to cause the mixture to run richer (more fuel) or leaner (more air) depending on how you are tuning your engine.  When removing this screw, it is important to first count the number of turns until the screw is tight. This will allow you to remember the setting when you return the screw after cleaning. Mine was set at 2 1/4 turns out which seems to be a fairly standard stock setting. I removed this screw after this photo. 

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After I took the carburetor apart, I soaked all of the individual pieces in Marvel Mystery Oil and then later sprayed all parts clean with carb cleaner spray. I used compressed air and carb spray to make sure all passages in the carburetor body were clear and clean. I took particular care to make sure the jets were clear  and open. I rebuilt the carburetor, making sure no rubber gasket seals were broken. Luckily all were intact. 

This is a regular part of scooter maintenance and one of my first steps in getting a scooter running after bringing it home.