Fuel pump rebuild

1989 Mercury, 35 HP, SN# 0C120583
This Merc has the "square type" fuel pump.
I purchased a Merc rebuild kit, # 21-857005A, and proceeded until I discovered ambiguous instructions as to how to proceed.
This has to do with the two check valves.
In my factory Merc manual it shows each valve assy as being a 3 part assy, a rubber disc. a nylon disc and a nylon retainer.
The rebuild kit does not contain the rubber disc nor is it mentioined or shown in the rebuild instructions. Also it does not instruct to discard the rubber disc, only to discard the rubber retainer, if you have one. The valve assy is then shown as a 2 part assy, nylon disc and nylon retainer.
It appears to me that this pump has been rebuit before because it does have the nylon retainer, the rubber disc and the nylon disc. Frankly, it looks kind of odd to me.
I know there are a lot of smart folks out there on this forum.
HOW SHOULD I PROCEED???
Thanks,
John

Re: Fuel pump rebuild

Were you having fuel delivery issues since you've had the motor? If so then obviously the previous owner did something wrong. My check valves have rarely gone bad in my motors. All I do is change the gasket around the checkvalve. If you blow into the valve, it should 'pop' out of place, and then pop back in when you cease to blow in it.

Re: Fuel pump rebuild

Pete,

I was not experiencing fuel pump issues to the extent that the engine ran fine on the muffs to mild mid throttle (a guesstimate, no tach attached). I decided to rebuild the the carb & fuel pump as preventative maintainence hedges since I bought this engine as a "parts engine" which had been sitting for some time. My main interest was the power tilt and trim. As I startined exploring "what works" on this engine I discovered thet everything works well on this engine and it runs quieter than the other 35 I currently have on my boat. The rebuild kit tends to make me believe that Merc decided that the rubber discs were no longer needed and that the nylon disc alone will provide a sufficient seal. I'll try your blow in, blow out, test on the valve.

Thanks,
John

Re: Fuel pump rebuild

Very often Mercury makes one of their parts obsolete, and make a newer, better aftermarket replacement. I would just swap out the old with the new and then give her a try. It only has one fuel pump. It is not like a 200hp motor that can have up to 4 fuel pumps!! A little trial and error here may just save you a big headache.

Re: Fuel pump rebuild

http://www.ebay.com/itm/21-42990A4-..._Accessories_Gear&vxp=mtr&hash=item5891e93ee0

You're original part number was 21-42990A4 before superseding upward, Does the photos in the link above look more like what was in your fuel pump when you opened it up?

Re: Fuel pump rebuild

Fun Times

The photos of the kit in the link you sent shows all the parts that are now in my fuel pump as I opened it up, including the 2 rubber discs (upper right corner). My newer kit (21-857005A-1, package dated 2002) does not have these rubber discs. I am going to proceed wiithout the rubber discs based upon the evidence of the superseded kit vs the newer kit.
Thanks for your help and thanks to all who replied.
John

Re: Fuel pump rebuild

The rubber disc are no longer used.When installing the retainers do not over compress them as the plastic disc will distort it's shape.

Works fine with just plastic disc check valve. June 2023