Scott Atwater fuel pump question ….

[huntleybill]

In order to keep this SA running, (1957 7.5HP 3375) I had to keep squeezing the bulb. So I rebuilt the fuel pump and I have the same result. So I pulled the hose from the carb and spun the motor over with a drill. The video shows the results. I have no idea how to tell when a fuel pump is pumping correctly because I have never seen one working so I though I would ask you.

Is this normal? Seems kind of week to me.
Your input is appreciated.
Thank you
Bill

https://youtu.be/XPdH1VQBvoQ

[dave-bernard]

looks weak to me. I don’t know how fast you are turning it .

[huntleybill]

Thats what I thought. The drill turns it as fast as a high idle at least.

This is the kit I got for it: https://www.ebay.com/itm/Scott-Atwater-5hp-7-5hp-10hp-Oliver-K2-K3-16hp-Outboard-Fuel-Pump-Diaphragm/202417855506?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

Any suggestions?

[Mumbles]

Is that an original S/A fuel pump repair kit? They went out of business over fifty years ago and if the diaphragm is that old, it’s probably gotten stiff from old age. It should be nice and soft, like uh, whatever.

[huntleybill]

It was a new kit. Diaphragm was soft and flexible. Most likely, fits other things besides SA’s. If this is not the right kit, where would a person get one?

[frankr]

Why not end the guessing and beg, borrow, or steal a fuel pump pressure gauge? Tee it in between the pump and carb and observe the pressure while running. Should show somewhere around a couple of PSI. Gauges are not expensive, usually combined with a vacuum gauge (for cars). Not to be confused with high pressure gauges for fuel injected cars.

[Mumbles]

What’s the height between the pump and the tank? Maybe try lifting the tank a bit by placing it on a box or something and see if the pumping improves. If it doesn’t, there might be a problem downstream from the pump to the tank.

A pulse operated fuel pump can only lift fuel so high and I believe around 30″ is considered OK for an outboard motor but don’t quote me on that figure.

If you can tee into the fuel line, prime the carb and start the motor to see how much fuel is being pumped under operating conditions. A few feet of clear plastic tubing attached to the tee and held straight up will give an indication of the pressure or volume the pump can develop. If it pumps well with the end of the hose placed in a container, the pump is probably OK.

• This reply was modified 5 years, 2 months ago by Mumbles.

[dave-bernard]

how are the check valves ?

[seakaye12]

The flow seems decent. Hard to imagine a small engine needing more fuel than that. But; as Frank mentions….maybe the pressure is inadequate?

• This reply was modified 5 years, 2 months ago by seakaye12.
• This reply was modified 5 years, 2 months ago by seakaye12.
• This reply was modified 5 years, 2 months ago by seakaye12.

[Tom]

If you haven’t already, make sure the line between the pump and the crankcase (the one that moves the diaphragm) is as short and firm as possible. A long hose or one that’s really flexible won’t do it.

T

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