I've replaced the mechanical fuel pump on my 700sci with cv products billet pump. It ran great all year. Doing winter maintence I found fuel in the oil. Pulled the pump and disassembled to replace the gasket. Cv products offers several springs for this pump. I was wondering if too high pressure at the mechanical pump could be part of the issue I'm having.

Does anyone know the specs on the stock mercury pump. I've even checked my factory service manual and can find he answer

Thanks. Mark

All mechanical fuel pumps leak small amounts of fuel. No flexible material is completely impervious to gasoline. That is why the oil must be changed.

Many run the stock merc pump you have in carbed applications and thus have checked fuel psi. 6-8psi is the norm, Mine ran right around 7psi. Remember, carb'd is deadheaded. Your FI uses the mech pump for volume, therefore it's preset shut off pressure (spring psi) is not of much concern. My opinion.

Thanks for the info guys.

Mark

just a poor design and you need to keep a eye on the lube, happens all the time..

I added this pump with the hopes it would solve that problem. It did not. Only cost 20 buck to replace the diaphragm. I think I'll also add a drain in the oil resovoir of the sea water pump to make maintence a little easier.

Thanks guys

Mark

Does the mechanical pump supply an electric pump? How many GPH is the electric pump rated at?

Yes in his application. The mechanical pump is there to basically prime the electric pump. Electric pumps don't like to pull air and fuel, whereas the mechanical pumps are better suited for that. Once the electric pump is primed , it just pulls fuel through the mechanical pump.

That is what I'm thinking of doing for my new fuel system on my boat when i convert it to efi. I have 3 tanks, ( 2 saddle tanks and one main center tank) I was thinking of letting the mechanical pump pull from the appropriate tank and feed it to a electric fuel pump. Then have the return from the fuel rail going thru a fuel cooler and back around to the front of the electric fuel pump. How many GPH is the stock mercury mechanical pump? My engines are twin turbo 454's probably making about 650 hp.

That sounds like a good plan. The Merc sea pump fuel pump is used on the 700sci. So you should not have a problem there. Fuel pumps are rated at free flow numbers , which messes alot of people up. The only reason to know free flow is as in your case a draw thru setup or to rate it against competitors pumps.It would be very hard to give a real GPM number because of different setups ie. fuel line sizes length of draw bends in lines etc.. If you really wanna know what that pump is free flow rated, I do believe they used a carter pump.