mec force 90 dual stage fuel pump

[kend301]

I have a 1994 Sport Jet 90 by merc / force , I went to put a new diaphram in the fuel pump and in the first stage there is a spring and washer assy not shown in the shop manual , the way it mounts it is all but impossiable to get the diaphram flat with the spring in , Looks like I will tear the new Diaphram by the bolt holes. Do I need this spring / washer ? It is not shown or mentioned in the factory manual but is on the parts diagram on boats.net

http://www.boats.net/parts/search/M...0 THRU 0E080399/FUEL PUMP ASSEMBLY/parts.html

I am talking about part # 12 and # 7

 

[roscoe]

Re: mec force 90 dual stage fuel pump

These parts were added to later models as an improvement.

 

[kend301]

Re: mec force 90 dual stage fuel pump

So if it was an " upgrade" it can be run without them ?

 

[roscoe]

Re: mec force 90 dual stage fuel pump

yes

 

[JAKER95XR]

Re: mec force 90 dual stage fuel pump

I have a 96 sport jet with the exact fuel pump.I have replaced the diaphram three times.My Merc. manual says to stick a putty knife between the diaphram and the gasket put the bolts in,tighten down.This works great.If the spring #12 and the washer #7 were not there what would make the suction to pull the fuel?Just a question.

 

[pnwboat]

Re: mec force 90 dual stage fuel pump

The pulses from the by-pass port which is fed through the small hole in the by-pass port cover and the hose from the crankcase acting against the diaphragm is what makes the fuel pump work. The one-way check valves keep the fuel flowing in one direction inside the pump and out to the carbs. Looks like the spring and washer (item #7 & #12) on the modified version positions the diaphragm to maybe push more fuel with each pulse.

NOTE: I installed the newer square type Mercury fuel pump on an old 1988 125 HP motor. I got a used by-pass cover and fuel pump from a later model motor on-line. The by-pass cover bolt pattern and size are the same for many of the motors. Just need one that matches up to the correct type of fuel pump. The newer square pumps have a different type of check valve(s) and they are included with the re-build kits. Plus the rebuild kits are cheaper for the Mercury style fuel pumps.

 

[kend301]

Re: mec force 90 dual stage fuel pump

Jaker95 , Thanks for the advice , worked great .. Kinda .. My wife was not impressed with my new use for the cake iceing knife