Severe flooding can show up as gas overflows over the top.
This is a list of possible causes:
- The most common problem is the needle & seat not closing. For new needle wipe with mineral spirits to get the black residue off. Needles are often damaged by people putting pressure on them while adjusting the float. Any marks on the viton tip indicates a bad needle.
- Fuel pump pressure is too high. New pumps are especially suspect. Check your motors manual for the correct pressure, but most will be 5 lbs, or less. Some are as low as 2 lbs. so be sure to find the specification for your engine.
- Dirt in the carburetor - dirt may be in the needle & seat. This can happen even if you just cleaned the carburetor.
- Parts of the old seat gasket left in the carburetor.
- Damaged viton tip on the needle. Any pressure on the needle while adjusting the float will cause this. Happens often.
- Bad float. For non brass floats, replace them anytime you can get a new one.
- Cracked housing under the seat.
- Power valve stuck open. This would more likely cause a very rich condition as opposed to outright flooding.
- Clogged gas tank vent, or no vent. You may have put on a non vented gas cap.
Don't skip any of these. Most people assume these things are OK, spend big money on carburetors and other repairs just to realize it's one of the items in the list.