Flooding or leaking in the Carter W1, WA-1, WO, and WDO carburetors
High fuel pump pressure. Test your fuel pump, most 1-barrels require 3.5-4psi. If your pressure is too high, add an inline pressure regulator and dial it back.
Leaking gas line, or connections. Connections could be cross threaded or loose in the bowl. Most inlet fittings require a gasket.
High float level: check specification table and float setting
Stopped up vent hole: some have a vent hole in bowl cover, others in the air horn leading into the bowl chamber.
Bowl cover not sealing or poor quality gasket: check for warping in the bowl cover.
Poor gasket on needle/seat or needle/seat loose in carburetor. Anything under needle/seat gasket preventing seal at bowl cover. Check for old gasket residue, cracks under the seat, or debris between needle and seat.
Worn needle and seat where you can see or feel a ridge on the needle tip. Sticky intake needle. The assemblies come in matched pairs, don’t swap parts around. Be careful when adjusting the float not to put pressure on the needle.
Ridge worn in the float causing intake needle to bind. This can be smoothed off my using a piece of sandpaper or emery cloth about 1/4″ wide. Rest emery cloth over the lip of the float by placing your thumb on top of it, pull the cloth through and that will smooth off the lip of the float. Do not use a file!
Float pin or holes in float bracket worn. This will cause float to bobble with end result being flooding. Replace both the float and float pin.
Check to be sure float does not bind in casting.
Cracked casting, passage plugs or parts not sealing gasoline tight in casting.
Dirt or paint under copper washer preventing gasoline tight seal in casting.
Gasoline leak at nozzle where it seats in casting due to poor quality gasket or nozzle not seated tight.