Fuel filter(s), Merc 120

[mfelthousen]

I have a 1977 Starcraft Holiday 18 I/O, with the Mercruiser 120. I splashed it for the first time this past weekend, and after about 1.5 hours of running I started to have fuel delivery issues (as I expected, after it sat so long). As part of my restoration I had removed the tank and dumped most of the fuel out of it, and then filled the tank with fresh gas, but I knew I could still expect debris to be an issue. My original plan was to run it a bit and replace all filters.

The boat does not have a water separator yet (I have one to install). It does have an inline clear filter before the carb (which is brand new), and a fuel line with a primer bulb, both of which I understand is not appropriate for an I/O. But, both helped me figure out what was happening, and get off the lake. The inline fuel filter was dry each time the engine cut out, after a few minutes of running. Using the primer bulb I could fill the filter again, and run for a few more minutes. I later found a crack in the hose leading to the inline filter, so I know my problem was mostly an air leak. I plan to replace all hoses between the tank and carb, and eliminate the primer bulb (but after my experience, will probably keep one on the boat for an emergency).

When I went to replace the filter on the pump I found that a previous owner didn't have one in there. I didn't realize at first that there seems to be two sizes, and the commonly available size (Sierra 18-7784) is smaller than the bowl on my pump. I've ordered a Quicksilver 49088Q2, and hopefully that'll fit more securely.

So, my question is, I see some posts saying that there should be an inline filter, but I haven't found one that is USCG approved for an I/O. When I am done with repairs, I will have the water separator, then the fuel pump filter, and then the carb filter. Other than losing a sight 'glass', would there be a purpose for this inline filter?

Thanks, Mat

 

[alldodge]

There was an metal inline filter installed on some EFI motors, but none on carbs. Someone cut the line and installed the plastic inline probably to help keep junk out of the carb. The pump/filter you have is the correct one but my guess is its not working and needs replaced. To verify place a pressure gauge on a Tee to check

 

[kenny nunez]

There is also a small spring that fits on top of the fuel pump filter that you may have to improvise. There may be an additional filter in the suction tube that is in the tank. The tube could be fixed in the tank of comes out with the 90* fitting, whichever way one may be present remove it by shoving a piece of wire through it. If there is a anti siphoning valve be sure it is clear and try blowing through it from the tank side to marke sure the ball is free to move. In the mean time try to order a new fuel line or if it is no longer from Mercruiser and there is a hydraulic hose shop in your area have one made. If you have the ability to work with steel tubing you might be able to make a new one using the old fittings.

 

[Alumarine]

There should also be a filter on the carb inlet.
Sierra 18-7859 or merc 35 49088T

 

[mfelthousen]

Thanks everyone. Getting rid of the plastic inline filter, replacing all new hoses, and installing new filters for water/fuel and at the pump seems to have addressed the starvation issue. I'll know for sure when I'm back on the water. I'm pretty sure the cracks in the hoses for the inline filter were creating the starvation problem. The pump itself seems fine since it didn't take much cranking to start the engine (I didn't prime anything).

Mat