Page last updated July 17, 2008



Carburetor Schematic

Mercury 700 Fuel System Maintenance

OK, here we have an old Mercury 700 circu 1977. The fuel system required that I replce all hoses, replace gaskets on fuel pump. It has a thin diaphram and the left side of engine has another huge gasket that was leaking lots of fuel to the outside area.

Powerhead is off but does not need to be for this project.

The leftside of engine had very little corrosion. All corrosion seems to be concentrated on right side. SO, all bolts came off with ease and were still in good condition. The bolts and bolt holes required very little cleaning and I could already hand tighten alomost all of them. No problems there.

I removed cover and inspected bore. Pistons have a little carbon coat at the spark area. I could not see any scarring in bore, so that was a good sign.

I took some chances by positioning block on its side. This makes it easier for contamination to enter piston bore and maybe you should not follow my lead in this area. You should have the powerhead in an upright position to avoid bore contamination. Make sure you place plastic inside bore to catch anything that may fall in.

FIRST things first!!! BE SAFE

Remove / disconnect all power supplies. No need to get electrocuted / executed.


Equipment needed:

  1. Basic tools - wrenches / wratchets / screwdrivers
  2. plastic organizer for various small parts (rubbermaid, etc)
  3. plenty of shop rags
  4. couple of plastic bags
  5. carburetor cleaner
  6. gasket remover (available in aerosol can)
  7. Gasket set for fuel pump and engine.
  8. gasket sealant, dressing / prep (needs to be for carburetor, fuel resistant)
  9. new fuel lines, various sizes based on removal (better to replace)
  10. compressed air (can or compressor)
  11. Safety goggles and breathing mask
  12. Copper tubing flattened and sharpened (used as a scraper)
  13. Patience

When all power has been removed follow the steps below.

1. Remove from left side, fuel pump housing. I had three bolts. You also need to remove electrical boxes that are in place. This can be tedious with lots of parts. Take plenty of notes on wiring, pictures as to their location. I will post pictures on that in a few days, I have to locate them.  
2. When area is clear, remove head bolts and notice fuel filter housing has a longer bolt. Notice the position of the housing and how the hose is attached. You will need to position it the same way during assembly.
3. Head bolts need to be unbolted slowly and carefully. Applying heat to this area is a risky proposition due to fuel contamination. Wash area with some warm soapy water so remove as much of the fuel deposits if you need to use a pentorch. Have a fire extinguisher handy just in case. They should be fairly easy and should not cuase a problem as this area is not expost to water or condensation as the right side where the water circulates through.
4. When cover is off, make an inspection and make sure you have no debris in this area. You will have to cover all cylinder bores with tape, plastic becuase this area will get messy due to the removal of gasket remnants. It is probably best to do this while the engine is upright so that no debris falls into bore area. My powerhead is off, so I went ahead and did it.

Lots of gasket left on. You can see where fuel was leaking through on gasket area.





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