Fuel pump doesn't pump

Captndrydock

Captndrydock

Seaman
Joined
Mar 9, 2020
Messages
68
I've been on a roll getting motors to run, but ran into another puzzler on a Force 125. I can't get fuel to pump past the fuel pump. The bulb is tight and squirts out the inlet hose to the pump, but once fastened to the pump, I get nothing.

I loosened the other ends thinking maybe an air lock, but no luck. I've turned the motor over thinking maybe it needed the cylinder movement to pulse the pump. Changed the diaphragm, same. Swapped out for another fuel pump, no luck.

Not sure about the procedure to test the fuel pump, I guess that's next. But the valves moved when I pressed on them... So for the moment, I'm stumped.

As usual, always grateful for ideas or solutions!
 
alldodge

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
41,981
I the pump mounted in the correct position?

Reason is my 125 has one pump and could be mounted "I think" higher and it would fit but hole doesn't go thru to exhaust. My 140 uses 2 pumps and there is a pump mounted in both places. Would need to go to the shop and look to verify
 
alldodge

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
41,981
Guess it's how you look at it. Web is saying vacuum pulses, your saying pressure pulses, and my original comment was thinking the same thing like a lawn mower. Either way thanks
 
R

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
37,709
The pressure pulse is bigger than the lower pressure ( some say vacuum ) pulse.----It is the PRESSURE pulse that drives the pump.---So much mis-understanding on such a simple device.----People just are not aware of how these pumps work.---That is why AMAZON sells so many of them.
 
Captndrydock

Captndrydock

Seaman
Joined
Mar 9, 2020
Messages
68
racerone said:
Pumps are operated by crankcase PRESSURE pulses.----Not so much by vacuum.
Click to expand...
Is this akin to blowing thru a straw vs sucking? Exhaust sucking pressure, Intake blowing?
alldodge said:
Guess it's how you look at it. Web is saying vacuum pulses, your saying pressure pulses, and my original comment was thinking the same thing like a lawn mower. Either way thanks
Click to expand...
alldodge said:
I the pump mounted in the correct position?

Reason is my 125 has one pump and could be mounted "I think" higher and it would fit but hole doesn't go thru to exhaust. My 140 uses 2 pumps and there is a pump mounted in both places. Would need to go to the shop and look to verify
Click to expand...
Yeah not too sure myself on all that, but thanks for your comment anyway. The fuel pumps are on the intake side. I'm guessing that intake is blowing or pulsing and exhaust is vacuum or sucking?


Love those 140hp's, hope to find one someday to rebuild or if I'm lucky to just tune up and run!
 
R

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
37,709
Fuel pump is mounted on the crankcase.----When piston comes down in the cylinder it compresses the air underneath it.-----This pressure in the crankcase is what drives the fuel pump.------When piston goes up in the cylinder the pressure in the crankcase drops.----The reed valves open and and let a fresh fuel / air charge into the crankcase.----It is nothing but a simple 2 stage air processing machine.-----And exhaust has nothing to do with operation of the fuel pump either !!-----Compression in the cylinder has nothing do do with operation of the fuel pump.
 
Captndrydock

Captndrydock

Seaman
Joined
Mar 9, 2020
Messages
68
racerone said:
Fuel pump is mounted on the crankcase.----When piston comes down in the cylinder it compresses the air underneath it.-----This pressure in the crankcase is what drives the fuel pump.------When piston goes up in the cylinder the pressure in the crankcase drops.----The reed valves open and and let a fresh fuel / air charge into the crankcase.----It is nothing but a simple 2 stage air processing machine.-----And exhaust has nothing to do with operation of the fuel pump either !!-----Compression in the cylinder has nothing do do with operation of the fuel pump.
Click to expand...
Thanks for explaining, always eager to learn more about how these motors work.
 
You must log in or register to reply here.
Top