2 bbl Carb

[Cksteiger]

I'm still puttin back together my 1986 4.3 L Merc. Replaced the long block with one that didn't have a mechanical fuel pump. I'll be using an electric fule pump now. The question - the old fuel pump had a site tube that ran to a fitting on the back of the carb. Do I just plug that fitting or does the carb need something coming in there to work properly?

thanks

 

[chiefalen]

Re: 2 bbl Carb

You will need a pump that gives between 4-6 psi. No sight glass is required.

 

[Maclin]

Re: 2 bbl Carb

Cksteiger,

The fitting on your carb is, I'm guessing, pretty high up and goes right into the top of the carb throat. It is there in case a mechanical marine fuel pump has a bad diaphragm, then fuel is pushed up that tube and into the airflow of the carb. Electric fuel pumps do not have or need this feature. Leaving it open at the carb should be fine, it will suck air a little but no biggie as it will not affect fuel metering. Block it off if you feel it necessary.

Now regarding electric fuel pumps, there are safety features designed into the wiring to prevent the pump from running on in the event the engine dies with the key on. It would be a good idea to wire in the safety features.

A quick overview:
An oil pressure safety switch is used to interrupt power to the fuel pump when oil pressure is below a certain psi. It plumbs into an oil pressure tap threaded hole. It is not the same thing as the sending unit, you need both items. There is also a 12v circuit that feeds the pump while the engine is cranking only. This covers the time when the engine has not started and oil pressure is too low to energize the oil pressure safety switch.

Look over the wiring diagrams for an electic fuel pump setup and familiarize yourself with the components and wiring run. You can search thru the threads here as Don S and others have provided the common Merc setup pics and diagrams many times.