Re: 1937er mechanical fuel pump
Posted by HH56 on 2022/5/22 20:31:14
The vacuum section of the pump is connected in series with the wiper motor. Wiper motor connects to the pump inlet side and manifold port connects to the pump outlet port. I don't know exactly where the supply port is located on the 37 manifold but there should be a dedicated port. Later engines had them on the manifold at the top front or rear or under the carb and there could be more than one. Most wiper only ports are 1/8" pipe size. Some carbs also have a vacuum port for the wipers at the bottom in the throttle plate casting.
1/4" steel tubing runs from the manifold (or carb) and wiper motor to the pump. Pump connections depend on the pump. Some have threaded ports that need fittings to connect the tubing directly and other pumps have hose barb type nipples and use a short length of vacuum hose to connect to the metal tubing going to the manifold and wiper motor.
Normal manifold vacuum will be stronger and in much greater volume than the pump will produce so the springs in the valves in the pump are overcome and valves are held open. Pump basically acts as a pass thru and diaphragm just goes thru the motion with nothing it can do. When manifold vacuum drops due to load or a wide open throttle down below what the pump can do the valves will then be able to close and pump takes over but at a reduced volume which is enough to keep the wipers moving but usually at a slower speed.
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