diaphragm fuel pumps, how much pressure?

[forgedin78]

1975 evinrude 15 hp....now searching out fuel problems. I think i might have a bad fuel pump, the top plug seems a lot oilier than the bottom, and I tried this: pulled hose off of carb, started motor, first nothing came out, then finally a little dribble, which continued until it ran out of fuel in the bowl and died.

How much pressure do these things put out, I mean i was expecting to see it go squirt squirt squirt, but maybe that was normal? anyone know what it should do?

running it in a tank, and sometimes if it starts to die, I will pump the bulb, and it will come to life again. All signs point to pump right?

 

[kfa4303]

Re: diaphragm fuel pumps, how much pressure?

yeah sounds like a bad pump. you may be able to get a rebuild kit for it. check here at iboats under the "marine store" tab. If not, you'll have to get a new pump, or try to scavenge one of off a donor motor. I just had a problem with the fuel pump on my old '66 20 hp and it turns out I had a slight air leak that caused poor fuel delivery. Once the leak was fixed it worked like a charm. Based on reading other posts I supposes you should expect (+/-) 2-3 psi from the pump.

 

[Will Bark]

Re: diaphragm fuel pumps, how much pressure?

You can buy a new fuel pump r4ight here at i-boats their part # 18-7350 for 51.99 which will save time and frustration of trying to rebuild. Good luck.

 

[laotou]

Re: diaphragm fuel pumps, how much pressure?

1 psi at 600 rpm. 1.5 psi at 2500rpm. 2.5 psi at 5000 rpm.

 

[F_R]

Re: diaphragm fuel pumps, how much pressure?

Don't trash the pump till you are sure there are NO air leaks anywhere between the pump and fuel level in the tank. Even the slightest air leak will prevent the pump from working properly. It is a pretty good fuel pump, but a lousy air pump.

 

[forgedin78]

Re: diaphragm fuel pumps, how much pressure?

ok so I'm hearing that it should put out roughly 2 psi. But what does 2 psi look like coming out the end of a fuel line? Hasn't anyone tried this before? I know if I squeeze the bulb while the hose is off it shoots quite a ways, but I'm assuming the bulb puts quite a bit of pressure onto a 1/4 line.

I guess tomorrow I will take the pump apart see if I can see anything obviously ruptured, and also check everything over for air leaks in the hoses.

If I need a new one, I will rebuild, There's no frustration involved lol, its a simple kit

 

[freddyray21]

Re: diaphragm fuel pumps, how much pressure?

with the hose off it should squirt a good stream out of the pump. like FR says though check for air leaks first.

 

[F_R]

Re: diaphragm fuel pumps, how much pressure?

Remove the pump from the motor, leaving the hoses attached. Now give the primer bulb a squeeze. If gas leaks out the hole on the backside of the pump, the diaphragm is shot.

 

[forgedin78]

Re: diaphragm fuel pumps, how much pressure?

Good idea, thanks. That will take a lot less time then disassembling the pump. So if it doesn't leak out the back, and you can blow through the inlet, but not through the outlet, is it good?
Or is it not that simple?

 

[boobie]

Re: diaphragm fuel pumps, how much pressure?

When you take the pump off to check for leaks, put some nuts on the screws that hold the pump on the mtr and tighten. If the pulse hole then leaks you have a bad diaphragm. Nut size should be 10/24.

 

[forgedin78]

Re: diaphragm fuel pumps, how much pressure?

well I took the pump off the motor, put nuts on the back and squeezed the bulb.......no leaks, not even a hint of one, is that the only test for a pump? I mean that shows the diaphragm is ok, but does that mean its definitely pumping?

Anyway, I finally realized that this thing is in a barrel, powerhead 4 foot off the ground and the tank is on the floor, so I set the tank up on a stepladder next to the motor, and I haven't had a problem since. Is it unreasonable to expect the pump to pull that much height? When its in the boat, the tank is only about 2 feet below the motor, if that. Is the pump just weak maybe?

By the way, I checked for air leaks, and I did have one slight one, that I fixed, but I still had trouble after I fixed it, until I raised the tank.

 

[RandyJ]

Re: diaphragm fuel pumps, how much pressure?

On some boats that is the fix. The fuel pump works off of the pulse and only a little pressure is created to move a very small amount of fuel with each pulse... extremely quickly. It just so happens that yesterday I was fishing and failed to open the vent on my gas tank. A very small vacuum was created inside the gas tank which resulted in the engine surging then dying. I simply was not mentally prepared for problems so took me a little while to realize what was wrong. The slightest pump on the primer bulb kept the engine running just fine... 1972 Johnson 25 hp on a 14 ft aluminum v-hull... it will scream with little weight in the boat!

 

[F_R]

Re: diaphragm fuel pumps, how much pressure?

Anyway, I finally realized that this thing is in a barrel, powerhead 4 foot off the ground and the tank is on the floor, so I set the tank up on a stepladder next to the motor, and I haven't had a problem since. Is it unreasonable to expect the pump to pull that much height? When its in the boat, the tank is only about 2 feet below the motor, if that. Is the pump just weak maybe?

By the way, I checked for air leaks, and I did have one slight one, that I fixed, but I still had trouble after I fixed it, until I raised the tank.

Aha!! I was wondering how high you were expecting that thing to lift fuel. I'd say you found the problem. About 3 feet is max you can reasonably expect.