Q: My 1984 Ford Bronco has four on the floor, a 351 Windsor, and the stock two-barrel carburetor. I rebuilt the carburetor, replaced the fuel pump and spark plugs, and checked the timing. When I start the truck, it'll run for a second, then gas will start to bubble out of the vents on the carb. I checked the float level, fixed the fuel/air mixture, and double-checked the new fuel pump. What's going on? I can't figure this out.
A: The "Windsor" engine family is a significant piece of Ford history. The engines were introduced in 1962, built at the Windsor, Ontario, engine plant, and are still in production today. There aren't a lot of carburetor questions these days, but it's always fun to take a step back. While it's not the case when looking at electronics, today's fuel-injection systems are pretty simple mechanically compared with a two-barrel (venturi) carb. Carburetors are composed of a maze of fuel and air passages that enable delivery of the correct air/fuel mixture under a full range of load and engine speeds.
Back to your problem: Assuming you didn't install a fuel pump that puts out excessive pressure for a carburetor and the float level is correct, you probably have a small piece of debris caught between the needle and seat. The float (located in the float bowl) has the needle mounted on one end. As the float rises with fuel level in the bowl, it pivots and moves the needle down into the seat. This stops the fuel from entering through the seat. Once fuel is burned by the engine, the float moves downward, lifts the needle out of the seat, and allows fuel to enter once again. It's a basic valve setup, similar to a toilet. It's very common to get a small piece of something caught in the needle and seat. This prevents the needle from fully seating. Fuel enters the carburetor with no control, and gas overflows out the top. Get a new needle/seat, and any required gaskets. Replace the needle and seat, and recheck the float level. While in there, make sure the float still floats -- some do leak or become saturated. Also, take a fuel sample to check that there aren't any particles, which may cause a repeat of the problem.
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