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Fuel pump kit check valve diaphragm difference

S

sliales

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"50hp 1981 4 cyl. Original se

"50hp 1981 4 cyl. Original service manual & parts manual show only 1 check valve diaphragm used in the integrated fuel pump. the fuel pump kit for this motor (genuine Mercury replacement) now contains 2 of these diaphragms, 1 rubber and 1 not rubber ... tan fiber looking. The new pump exploded view shows both but not which one goes where. Same goes for the Sierra aftermarket kits ... they show both but not which one goes in 1st.
Anyone had this problem?"
 
"Re: Fuel pump kit: Note diff

"Re: Fuel pump kit: Note differences
288883.jpg
Use both? If so, in what sequence?
 
"Thanks for the reply JB, the

"Thanks for the reply JB, the problem is that I have been fighting fuel pump issues for a few years and has not run right all along mostly due to fuel starvation to 1 carb or the other. Originally there was only the rubber check valve diaphragm included in the fuel pumb kits and that is the way it came from the factory as well. Now they include 2 of them and they are of different material but never have I seen instructions on their order of placement. As you saw in that diagram you linked they simply show 2 of them labeled with the same ref number as if they were identical. I have tried using both and in different sequences but have had no success."
 
make sure your carb base gaske

make sure your carb base gasket is positioned correctly as to not block off the hole. Check compresion of the engine. Ask Graham (click on his name) he might have the factory manual on his computer.
 
Yes carb to head gasket positi

Yes carb to head gasket positioned with holes mated... 'been there .. done that' deal. Everything else is fine (new actually) and WOT while hand pumping bulb is 5200 rpm and starts great. Pretty certain problem is with check valve diaphragm(s).
 
"Sorry, didn't look at any

"Sorry, didn't look at anything bigger than a twin cylinder until about 20 years ago, so my earlier manuals (pre-1986 stuff) are all for smaller motors."
 
"Graham, I have the original f

"Graham, I have the original factory service and parts manual for this motor. They both offer no help as they only show the 1 check valve diaphragm. The pumps will supply fuel at low throttle when using only the black rubber cvd but will not pump when using both back to back in a sequence of tan then black going from inlet side to carb. when you reverse that sequence the pump will not work.
I am going to try just the tan one next. It is a real pain changing these out as that lower carb is not quick to remove (as you may have experienced)and the pump cannot be accessed with removing the carb; unlike the top one."
 
"I have zero literature on thi

"I have zero literature on this at all that I can find - even took a quick look through the service bulletins and nothing stuck out.

The only thing that even remotely comes to mind is, the "non-rubber" ones may be something like Merc's answer to the issue of E-10/15 fuel causing problems dissolving older rubber compounds - but that really is a "far out guess".

So their intent may have been "either/or", not both pieces..."
 
"Thanks Graham, that is pretty

"Thanks Graham, that is pretty much my conclusion as well ... I have never tried just the non-rubber one and will do so as soon as my other 'honey-do' list is satisfied.

Thanks again"
 
Back for a wrap up. Grahram y

Back for a wrap up. Grahram you were right on .. the non-rubber check valve diaphargam was included for use with blended gas. I installed it and not the rubber one and it works fine. My original fuel starvation problem turned out to be a loose fuel inlet to fuel pump so it was sucking air.
Thanks for all the responses. Engine now runs 5400 rpm at full trottle.
 
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