I have a 720 gas. the carb is leaking at the top of the fuel bowl. I think this would be above the normal level of fuel in the bowl and that it indicates a problem with the float. Or the shut off valve. How do I check it?
 
I would first check the oil dip stick to determine if excess gas is getting into the crankcase. Disconect the gas line at the carb & check if there is a flow of gas when the engine is shut off. Press down on the knurled knob on the top of the sediment bowl to determine if that affects the flow of gas. The carb float could have a hole in it allowing gas to enter and sink the float. Does the tractor start & run normally without a flooding condition? We need mor info.
 
It's been a few weeks since I ran it. It ran normally but started
leaking fuel. I shut the fuel off at the tank and ran the carb dry. Today I went to work on it, opened the tank valve and depressed the stem at the fuel bowl to fill the carb. After a few seconds it began leaking at the top of the bowl, more than just a drip. If the float were acting properly ,wouldn't it shut off the flow before it reached the top of the carb fuel bowl
 
The fuel level on a Duplex carburetor is right at the fuel bowl gasket. Odds are your bowl is deformed by someone putting the bottom gasket on in the wrong place. This gasket goes between the bowl and the carburetor on the inside of the bowl, not outside. A deformed bowl will cause a lack of pressure on the bowl gasket, causing your problem of leaking. The float won't shut off the gas flow because the leak gives the fuel someplace to go. Remove the bowl and get it flat on the bottom and you should be fine. Mike
 
I have seen the bowls missformed when the gasket was placed on the outside of the bowl stem instead of inside the bowl stem. Do as Mike suggested, remove the bowl,check & flatten the bowl bottom, install a new bowl gasket place the stem gasket over the stem, install bowl and tighten bowl nut.
 

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