The Rochester B series carbs are prone to leak around the two halves of the body due to warping. Overtightening of the bowl screws causes this. If the warping is minor you may get away with cross filing the surfaces. For more extreme warping you can create a jig, heat the body, and straighten it out with the right equipment. We’ve done this in the past, it’s a lot of work and honestly not sure it’s worth the trouble unless you really want to keep an original carb.
As a last ditch effort you can try two bowl gaskets stacked together.
This Zenith 228 carburetor was designed specifically to replace the manual choke Rochester B carbs and we highly recommend it as an alternative fix.
Get all the specs and more photos here.
Some of the things causing too much fuel to enter the carburetor.
Bad float, or float adjustment bad. Test the float by heating up some water and immersing the float. Any bubbles indicates a leak.
Needle & Seat not sealing. Turn the top upside down so that the float rests on the needle. Blow gently into the fuel inlet. You should not be able to blow by the needle & seat. Keep in mind that blowing over 4 - 4.5 lbs will cause the needle to open.
Fuel pump pressure. Should test 4 - 4.5 lbs. Higher pressure will force the needle open, letting gas go by. New fuel pumps are especially suspect. If all else fails add a regulator between the pump and the carburetor.
Dirty carburetor. Pull the top off of the carburetor. Any dirt, or corrosion at the bottom of the bowl indicates a dirty carburetor. Clean & rebuild the carburetor.
Power piston may be frozen, allowing fuel to flow through even at idle. You should be able to move the piston up and down freely.
Check ball, or spring may be missing from the power cap. The small check ball, then spring goes in the hole before screwing in the retainer screw.
Watch the video below for tips on what to look for when your carburetor is flooding.
There is no seal that seals the stem from the float bowl and that is where the fuel is coming from. Don't let this continue as it is a fire hazard.
Most likely the carburetor is warped allowing gas to splash out of the float bowl. That can be corrected if you can build the jigs for this to heat and squeeze the parts. Not an easy process.
It's also possible you are flooding. With a flooding situation, there would be too much fuel in the bowl. Flooding - is the exhaust burning black? Are the plugs burning black? Is there a strong fuel smell coming from the engine?