The mechanical fuel pump on 1976 to 2005 Mercury 135, 150, 175, 200, 225 HP 2-Stroke V6 outboards (Black Max 2.0 and 2.4 Liter and 2.5 Liters) is a crankcase-pressure-operated, diaphragm-type pump. Crankcase pulsating pressure (created by the up-and-down movement of the piston) is transferred to the fuel pump by way of a passage (hole) between the crankcase and the fuel pump.
Some symptoms of a bad fuel pump or restricted (lean) fuel flow include:
1 - Loss of fuel pump pressure
2 - Loss of power
3 - High-speed surging
4 - Preignition/detonation (piston dome erosion)
5 - The outboard cuts out or hesitates upon acceleration
6 - Outboard runs rough
7 - Outboard quits and cannot be restarted
8 - Outboard will not start
9 - Vapor lock
Remove, Clean, Inspect, Rebuild, Install:
1. Clean fuel pump housing, check valves, pulse chamber and pump base in solvent, and dry all but
check valves with compressed air.
2. Inspect each check valve for splits, chips, and proper sealing against the pump housing.
3. Inspect boost springs for weakness or breakage.
4. Inspect the fuel pump housing, pulse chamber, and base for cracks or rough gasket surface and replace if any are found.
5. Inspect the fitting on the fuel pump housing for loosening or any signs of fuel or air leaks. Replace or tighten the fitting if a leak is found.
6. Insert new retainer from the rebuild kit through plastic disc and rubber check valve.
7. Install new check valves and retainers into the fuel pump body.
8. With the new retainer installed in the pump body, break the retainer rod from the retainer by bending sideways.
9. Install the new rod into the retainer cap and, use a small hammer and punch to tap the rod down into the retainer until flush with the top of the retainer.
10. Place the boost spring into the pump body and place the cap onto the boost spring.
11. Assemble the remainder of the components as shown and install retaining screws thru to align.
12. Install the rebuilt pump onto the powerhead. Torque to 55 Ib. in. (6.0 N·m).
13. Install hoses onto proper fittings and secure them with straps.
14. Make sure you run the engine and check for leaks before launching the boat.