Carb is overflowing with gas

This is a Marvel Schebler TSX 871 on a D17.  I rebuilt the carb about a year ago with one of the $25 kits (new jets, gaskets, float valve, etc).  The float valve does not stop the flow of fuel to the bowl.  If I forget to close the sediment bowl when not using the tractor, the crank case will fill with gas.   I've put the proper .25 inch gap between the gasket surface and the top of the float.  Also, in the metal tab portion of the float, there was a little dimple from the shut off needle.  I filled the dimple with solder and filed it flat.  I've removed the needle from the valve and flushed the fuel passageway out.  Finally, I put the carb back on the manifold, attached the fuel line, and turned on the gas at the sediment bowl.  After 30 seconds, fuel was dripping out of the air inlet.

I would guess that the needle has the rubber/plastic tip. If you get one that was not (packed out) when being made (material injected into the tip mold) it will never seal.

When they first started making the needle with the plastic tips I had about half of them fail. (about six that failed)  back about ten years.  After a few years not many of the ones that didn't fail now leak. I shut off the gas to all my tractors when I shut them down now.
Most I let run the gas out and die then shut off the switch.
I have found that they can hold most of the time but when I decide to trust one it seems to have an empty tank when I need to use it.
I have eight tractors that I use from time to time but set most of the time.

More than likely the needle is viton tipped, metal needles do require a few hours of field service to get seated properly. I have seen many carbs that the viton tipped needles don't seal properly after a little use, they are fine while running but will get a slow leak when shut off. Certain floats are prone to cracking due to the shape when the halves of the pontoons are stamped. If you add to much solder your float will become to heavy. The rattle test is a good one as long as you don't hear a small bead of solder inside. I test floats by putting them in the freezer overnight then put them in pretty hot water the next morning and watch for bubbles. I always install a new float in my rebuilds , it saves a lot of headaches on down the road. I have been installing a small ball valve in the fuel line on my tractors. It is easy to flip a 1/4 turn ball valve on and off and not have to worry about the packing leaking on a sediment bowl that is hard to reach on some machines. I have seen the bowl vent on a carb get plugged up and cause a similar problem.  

When I work on a carburetor, I blow into the gas inlet and gently lift the float to see if it closes off the wind pressure I can blow. If it doesn't I look about a different set of needle and seat.

Gerald J.

Try opening up the float adjustment a tad.  The spec was set for original thickness of bowl gasket and original density of gasoline.  Things change over 50 years.  Gasket thickness may be different.  Gas certainly has changed as it has no lead, but does have lower boiling volatiles in winter and likely alcohol any old time.  This doesn't lift a float as well.  If it seals the flow at the seat you're probably good unless you find the engine really starved for fuel under load.

Paul, I interested in knowing how the crankcase will fill up with gas with an updraft carb.

A good practice to get into with carb rebuilding is burnishing the needle valve with some super fine steel wool so it slides up and down in the seat bore smoothly. Over the years of rebuilding carbs for myself as well as our customer's, I've found where the needles will hang up in the bore on occasions because of a little rough edge on the needle itself which will cause fuel to run out of the intake or out the bottom vent. Dirt in most cases is the cause of carb problems whether its debris from the tank, sediment bulb, or fuel line. Another area to check is behind the 90 degree inlet fitting. Dirt, rust and debris gather in the back of that inlet corridor. Incoming fuel will dislodge this debris on occasions, and it gets caught in the needle/seat causing havoc again. HTH
Steve@B&B