1996 Johnson 25hp Fuel Pump Question

[Ppopps]

Should the little white mushroom (or piston) shaped plastic piece internal to the fuel pump which is spring loaded and whose post sticks through the small hole in the back of the pump when the spring is compressed be poking in and out as the pump operates with the engine running?

My engine is running fine at idle but surges and oscillates when in gear and run anywhere above about mid throttle. I never see that white post stick out of the fuel pump unless I squeeze the primer ball hard then it comes out. Should it not pop in and out on occasion as the pump runs?

Anyone understand that explanation? Sorry....

 

[gm280]

I think you need to post some pictures because I'm at a lost to what you are asking...

 

[racerone]

Not all the pumps have that feature.----Does the running of the motor change / improve when someone operates the manual fuel pump?-----If not then I believe there is nothing wrong with the pump on the motor.-----These pumps are very reliable and often changed out for a last effort to find a cure.----Run with a timing light and see if you have steady spark at higher throttle settings.---Any chance the motor is running hot and going into a " fail safe mode ' in this case ?

 

[Ppopps]

Hi Racerone, my pump definitely has that white pin and it definitely comes out of the hole when I squeeze the primer ball until hard, but my point is that it never comes out of the hole after that with the engine running, I put my finger on the back side of the pump and it never pokes through. This has me wondering how the diaphragm could be pumping if the white post from this piece never pops out.

Regarding the spark, remember that on my motor if I squirt mixed fuel into the carb throat when it?s doing it?s funny business, running rough and surging, it picks right up and runs like a champ so I?m convinced it?s carb/fuel delivery that?s the problem.

I have cleaned the carb such that you could serve soup to the Queen from it, there?s zero chance of a blocked passage, I am certain of it. That?s why I?m now suspect of the pump.

Regarding using the primer while running, this is tricky for me to answer?.while squeezing the bulb I believe that yes I can make the motor run a ?little? better such that it won?t surge at mid throttle, only at high throttle, whereas without me on the bulb it surges for both, does that mean anything?

I took the pump all apart and it honestly looked fine and there are no fuel leaks, but it still runs the same so I am baffled. Have tried a new fuel hose and different tank too?.what the heck?s left other than new fuel pump internals (though I?m skeptical, like you, that this is it)?.hate to give up!

 

[racerone]

Post # 3 is very clear !!------Look for the real problem.---Perhaps run with a timing light to see if it is a spark issue.----Post a video if you can.----I can not recall ever installing a complete new pump to fix a problem with an outboard motor.---------Have seen many new pumps installed on motors by folks who are lost in the art of trouble shooting !

 

[Ppopps]

No Title

Can anyone tell me what the "wagon wheel" shaped thick gasket is that comes with Sierra Kit 18-7800? The picture below shows my fuel pump and all my old parts after rebuilding it. I couldn't find any use for that part (and only that part!) so I'm hoping someone answers that it's only needed for a different style of pump also covered by the kit? There were no diagrams with the kit, and I can't find much online.



Any help would be great! Darn hard to get that diaphragm seated well with no wrinkles given the internal springs!

 

[racerone]

The wagon wheel gasket was used with older style pumps.--Newer inlet cover used the o-ring.---Not to worry about seating the diaphragm as that thing has to flex while operating.--More mystery solved.