Fuel pump operation

[dingy]

I was going to post this in reply to a members fuel problems, but decided to start a new thread so it could be located later for reference.

 

Here is a bunch of pictures I took of a 1st gen fuel pump a week ago just for S&G's. The RSV is probably similar, but I don't know. Just offering this as maybe some help in understanding the mysterious fuel pump. It is not a really technical description below, but the basic operation.

 

In a nutshell, the pump operates by energizing a coil and pulling the plunger towards the contact end. This pushes in the contact assembly on the other end, breaking the current path to the coil. The plunger returns to rest position, contact closes & cycle repeats.

 

When the plunger pulls towards the contact, it pulls gas in from the tank into the pump cavity via a one way valve. On the Return stroke the fuel is pushed out another valve towards the carbs.

 

This happens until 1 of 2 things occur, first is pump builds up pressure in line and and the plunger does not return forward to complete pump stroke. 2nd is the fuel pump circuit times out after 4 seconds of not sensing motor running and cuts off current to pump.

 

On pump end there are two diaphragm type valves, one allows fuel to be pulled in to pump cavity, but not pushed back out. Other allows fuel to be pushed out towards carbs, but not flow back into carbs.

 

Not my best tech write up.

 

 

Gary

[mlew]

Does anybody make rebuild kits for these? The rubber check valves in mine are starting to crack, its making the pump run too much.