Force 120 fuel pump

tomdog1970

Cadet
Joined
Apr 12, 2009
Messages
10
I bought a boat before I deployed. It has a Force 120 on it. I believe a 93 model. I know it was not the original motor. I've fixed various problems on it, thanks to you guys. The thing has never run the way it should. I can't recall this thing ever running over 3 grand. Here lately It's getting even slower to plane out. Just this year I had to drain 15 gallons because of water in it. I started looking around and really trying to get this thing more reliable. During the process I've noticed #4 cylinder is not burning the gas. I done everything I've read. I did a compression check because I kew that would be the first question. 110, 110, 130, 125. I put inline spark testers on it and they all are firing. I've pulled all plug wires while it's running and all changed audibly except # 4 and it stayed constant with no change, and it's firing trust me. The new plug though looks as if it has never been fired. I swapped it with # 1 and can now see firing marks on it. I also swapped the coil out with # 2 with no difference. I kept reading, so I pulled the fuel pump to look at the diaphragm (didn't want to). Well it was torn. I just ordered 4. My question is: How in the world will this affect the cylinder if it still has some fuel to burn in it? Will this be the end of my problem? Thanks for any help.
 

pnwboat

Rear Admiral
Joined
Oct 8, 2007
Messages
4,251
Re: Force 120 fuel pump

The fuel pump works from the intake pulses in the crankcase. I think the pulse hose on the fuel pump is connected to the crankcase for number 4 cylinder. If the fuel pump diaphragm was torn, it could be dumping fuel into #4 cylinder flooding it out? I don't know but replace it and see how she runs. I have to say though, typically a plug that looks brand new after running is usually due to lack of spark or weak spark. But you never know.
 

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,765
Re: Force 120 fuel pump

The fuel pump works from the intake pulses in the crankcase. I think the pulse hose on the fuel pump is connected to the crankcase for number 4 cylinder. If the fuel pump diaphragm was torn, it could be dumping fuel into #4 cylinder flooding it out? I don't know but replace it and see how she runs. I have to say though, typically a plug that looks brand new after running is usually due to lack of spark or weak spark. But you never know.


Exactly.

Totally flooded out the #4.

The failed diaphragm is a result of age, and ethanol in the gas.

The new diaphragms are ethanol resistant.
 

tomdog1970

Cadet
Joined
Apr 12, 2009
Messages
10
Re: Force 120 fuel pump

You nailed it pnwboat! Thank you! I have yet to check RPM's but # 4 is back online. Thanks again.
 

pnwboat

Rear Admiral
Joined
Oct 8, 2007
Messages
4,251
Re: Force 120 fuel pump

Hey, even a blind dog finds a bone once in a while!
 
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