Flooding - Too much fuel in the float bowl.
Gas pouring out the top of the carburetor is a sign of flooding. Gas leaking out of the throttle shaft is also a sign of getting too much gas.
Gas flows down the carburetor bore. When there is too much gas it will run out anywhere it can. The throttle shaft is a natural conduit.
Things to check (not in any order):
Fuel pump pressure - check it for 4 lbs, or less. Too much pressure will hold the needle open and allow too much fuel in the bowl.
A defective needle - A damaged needle, which can be damaged when setting the float. Be sure not to put any pressure on the needle. Check the viton tip for any marks. Also wipe the viton tip off with mineral spirits to remove the black residue.
Float level - Test the float. The Nitrophyl float must be weighed for proper weight. The floats are not hollow. There are 2 different floats for this carburetor.
Check the seat for a gasket and make sure there is not double gaskets, or a damaged gasket.
Look for cracks around the seat which would allow fuel to come in around the seat.
Blow into the fuel inlet with the needle closed to see if it is leaking by.
Any sign of dirt in the bottom of the float bowl is a problem. Dirt may be going by the needle. Change the filter, clean the fuel lines & the gas tank.
Dies at Idle Due to Excess Fuel
At idle look down the carburetor. Is gas dripping into the bore from the main discharge. The main discharge is where the gas comes out when accelerating. If it is, then there is a problem in the discharge somewhere.
Check the check balls in the economizer block. They need to be clean and loose.
Check the back of the economizer block to make sure it isn't warped. You can run a flat file over the surface to be sure.
Remove the idle mixture screw and while holding the small inside the bore closed, blow air into the screw hole to make sure the idle vent hole is clear.