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125 force fuel pump question

altitude 411

New member
I'm trying to get my 125 Force to run properly if that is possible after complete rebuild. :confused: I believe the fuel pump may be overactive... I pulled the third cylinder spark plug and it is super clean, no carbon build-up like the other plugs. Fuel pump freshly rebuilt with gasket, diaphragm, check valve. How do I confirm it is operating correctly? I have read that it can wash #3 cylinder, but not sure how to diagnose. I have a stumble at idle and a rich attitude when revving engine. Carbs are freshly clean and rebuilt. A/F adjustment is 1 1/8 turns. Timing is 28 static, correct? I've heard 28, 30 32??? what do the members of the asylum say is best? Thanks for any help
 
Last edited:
Follow the static timing.
The stumble at idle?? try a starting fluid test:
Start motor and spray Starting Fluid around the
intake side and under the coils and packs.
If spraying makes a difference?? then it's sucking
air someplace.

One clean plug: not sparking, bad diaphragm??
Do a compression and spark test on each cylinder.
 
Thanks Jerry. Is the best static timing setting 28 BTDC or 30? I've checked compression after rebuild. Compression is good and consistent across all cylinders and good spark as well. I've replaced all components of fuel pump with new. New diaphragm. Question is there a way to test flow rate of the fuel pump to tell if it is pushing too much fuel into cylinder #3? After running engine for 30 minutes or more, the #3 plug has no carbon build up on the electrode like the others...
 
set at 28
The only way to test the diaphragm is to check for
holes and tears.

Start the motor and pull the spark plug wire and see
if that makes a difference in the way it runs?
 
I read (I believe it was one of Franks old posts) about the fuel pump on these 125 Force motor sometimes pushing too much fuel and washing out #3 cylinder. It didn't state how to resolve the problem unfortunately. The diaphragm is intact and freshly replaced. I was hoping there was a way to check the check valves or??? I need to do some more research on the mechanical fuel pump for this engine. I know there is a couple of different options for the Force. One has a spring (which mine has ) and the other does not. I don't know what the differences are other than that or which option my motor should be running. My motors serial # doesn't register with any model year for parts on this website or any other website that I have tried. Very frustrating but it is par for the coarse with this engine. I'd tie a rope on it and throw it overboard for an anchor but it would likely fail that as well... I'll keep trying (to fix) and report back. Seems like you are the last of the Mohicans on Force diagnosis Jerry but I see even you run a Merc:D
 
I went to the Mercury because I wore the Forces out.
Almost 30 years in salt water was too much for the transom
and the aluminum used in the mid section.
Both motors were running when I changed.

About the check valves: in all my years I ran into only one
check valve that was bad.
I was doing the routine maint. of changing the diaphragms.
Opened one of the pumps and the check valve fell apart.
Still worked but came out in pieces???
 
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