Insert a "tee" at the fuel inlet.
The following from the troubleshooting section of my website:
Jon
A common complaint today is fuel dripping out of the throttle body by the throttle shaft AFTER the engine is switched off. While a number of issues may cause this problem, by far the most common issue is the volatility of modern fuel. Mechanical fuel pumps have a check valve which prevents fuel from moving back to the fuel tank. The problem is as follows:
(1) After the engine is switched off, heat from the engine heats the fuel in the fuel line.
(2) The expanding fuel (increased volatility) creates pressure in the fuel line from the pump to the carburetor.
(3) The check valve prevents the fuel backing up through the fuel pump.
(4) The pressure increases to a point the float/fuel valve combination in the carburetor cannot withstand the pressure.
(5) An amount of fuel (usually from a teaspoon to a couple of tablespoons) flows into the fuel bowl of the carburetor.
(6) This raises the fuel level in the bowl above the main discharge nozzle(s).
(7) Fuel flows through the main discharge nozzle(s) and drips onto the throttle plate(s) which is/are closed, and exits out beside the throttle shaft(s) dripping onto the intake.
Possible solutions:
(1) IF POSSIBLE, AVOID ETHANOL LACED FUEL! Sometimes you can buy real gasoline at a marina
(2) Buy the lowest octane name-brand fuel that does not ping or detonate in your engine (the higher grades often have more ethanol)
(3) Install a “vapor return line” (take a look at return lines used on many factory air-conditioned cars)
(4) Learn to live with the issue.
