Description
Overtime with working on the engine of your car. These overflow tubes can get bent up and kinked or even worse cut too short. The tubes are very import and must be kept the proper length. The pipes are open to the atmosphere for two main reasons. First and most importantly they allow incoming fuel to push out the air inside the float bowl so the fuel can quickly reach the correct level. Second, if the float valve (also known as the needle and seat) sticks open often due to a small piece of debris the fuel will flow out through the overflow pipe and safely away from the engine. Without this escape route, the excess fuel would spill into the carburetor and enter the engine.
If too much liquid gasoline enters the engine, not all of it will vaporize before the spark plug fires. The fuel that does vaporize will make the mixture overly rich like when the choke is stuck on causing the engine to run poorly and emit black smoke from the tailpipe. Eventually, the engine may flood and stall, which could lead you to thinking you have a bad fuel pump or the carburetors would need to be rebuilt. But worse if any liquid fuel that reaches the cylinders can wash away the protective oil film on the cylinder walls and drain into the crankcase. If this happens repeatedly, it can lead to increased engine wear. Gasoline in the oil also thins it out, so the oil should be drained and replaced as soon as possible. Inspect these vent tubes during every valve adjustment to insure the are in good order. Cross Reference 451-250
