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Howdy,
First post here, so please be gentle. I have a 1986 Mercury 75HP 4 cylinder two cycle motor, SN 0A994929. It has a triangular fuel pump that is now listed as obsolete, but diaphragm kits and internal parts are still available.
When I purchased the motor, it has sat up for a long time without being ran. I decided to go ahead and rebuild the carburetors, replace rubber hoses, etc that may have dry rotted due to age and lack of use rather than risk clogging a carb with rubber debris. I didn't rebuild the fuel pump initially, but want to go back and do so after test running the motor on the lake. Here's the results of the test run:
Note: Fuel tank is new, buld and all gas lines and filters from tank to fuel pump are new. Gas was fresh gas (bought near lake, no alcohol) with new Merc Quicksilver two cycle oil mixed using ratio recommendations for this motor. Only old part was fuel pump. Stator and trigger assembly are new, replaced due to wiring damage done by dirt dobber chewing up wires and shorting them, then original owner tried to start motor and fried wires so wires could not be repaired. Rectifier was also replaced, due to corrosion caused by dirt dobber mud. Compression test got 135 PSI on all cylinders and original spark plugs looked brand new when removed from motor for inspection and pre-oiling of cylinders with two cycle oil/carbon cleaner mix for storage while I was restoring the boat the motor came with.
Motor ran extremely strong on first day test, but was unable to check if motor had correct prop due to loose wire on tach. Fixed loose wire, reran test next day. Motor ran strong cold for about 200-500 yards, but began to have acceleration problems when comes accelerating from stop at WOT or when going from low rpm (2000) to WOT. Motor would bog out and would no longer run at WOT without stalling. Motor acted starved for fuel. I realize this may be a fuel issue or it may be a electronics/electrical issue even though the stator and trigger are new. So I'm looking for suggestions as to how to proceed as well as doing simple, inexpensive things that will eliminate other potential issues.
Motor had problems above 200 rpm, but would "chug" along at 2000 rpm and trailered okay.
I am now looking at getting parts for the fuel pump. The triangular fuel pump this motor has on it are now listed as obsolete, but internal parts are available from Mercury and aftermarket (sierra/mallory).
Here are my questions:
1. It is possible to replace the triangular fuel pump with the more common and still available square fuel pump? If yes, what parts are needed to do so beside the fuel pump?
2. If no to question 1, what parts should I buy for the triangular fuel pump and are the OEM parts any worse/better than the after market parts?
3. The OEM part number for the triangular fuel pump diaphragm assembly is 55278A 5, but doesn't list what it comes with. Does it come with a diaphragm, two gaskets, 1 o-ring and two seals?
4. If I'm working over the triangular fuel pump, what parts should I replace as "good practice" for doing a quality job? Just the diaphram assembly and the check valve assembly?
My apologies for so many questions. I'm pretty mechanical, as my Dad was a mechanic and I've rebuilt lots of things, but I'm not experienced working on boat motors.
First post here, so please be gentle. I have a 1986 Mercury 75HP 4 cylinder two cycle motor, SN 0A994929. It has a triangular fuel pump that is now listed as obsolete, but diaphragm kits and internal parts are still available.
When I purchased the motor, it has sat up for a long time without being ran. I decided to go ahead and rebuild the carburetors, replace rubber hoses, etc that may have dry rotted due to age and lack of use rather than risk clogging a carb with rubber debris. I didn't rebuild the fuel pump initially, but want to go back and do so after test running the motor on the lake. Here's the results of the test run:
Note: Fuel tank is new, buld and all gas lines and filters from tank to fuel pump are new. Gas was fresh gas (bought near lake, no alcohol) with new Merc Quicksilver two cycle oil mixed using ratio recommendations for this motor. Only old part was fuel pump. Stator and trigger assembly are new, replaced due to wiring damage done by dirt dobber chewing up wires and shorting them, then original owner tried to start motor and fried wires so wires could not be repaired. Rectifier was also replaced, due to corrosion caused by dirt dobber mud. Compression test got 135 PSI on all cylinders and original spark plugs looked brand new when removed from motor for inspection and pre-oiling of cylinders with two cycle oil/carbon cleaner mix for storage while I was restoring the boat the motor came with.
Motor ran extremely strong on first day test, but was unable to check if motor had correct prop due to loose wire on tach. Fixed loose wire, reran test next day. Motor ran strong cold for about 200-500 yards, but began to have acceleration problems when comes accelerating from stop at WOT or when going from low rpm (2000) to WOT. Motor would bog out and would no longer run at WOT without stalling. Motor acted starved for fuel. I realize this may be a fuel issue or it may be a electronics/electrical issue even though the stator and trigger are new. So I'm looking for suggestions as to how to proceed as well as doing simple, inexpensive things that will eliminate other potential issues.
Motor had problems above 200 rpm, but would "chug" along at 2000 rpm and trailered okay.
I am now looking at getting parts for the fuel pump. The triangular fuel pump this motor has on it are now listed as obsolete, but internal parts are available from Mercury and aftermarket (sierra/mallory).
Here are my questions:
1. It is possible to replace the triangular fuel pump with the more common and still available square fuel pump? If yes, what parts are needed to do so beside the fuel pump?
2. If no to question 1, what parts should I buy for the triangular fuel pump and are the OEM parts any worse/better than the after market parts?
3. The OEM part number for the triangular fuel pump diaphragm assembly is 55278A 5, but doesn't list what it comes with. Does it come with a diaphragm, two gaskets, 1 o-ring and two seals?
4. If I'm working over the triangular fuel pump, what parts should I replace as "good practice" for doing a quality job? Just the diaphram assembly and the check valve assembly?
My apologies for so many questions. I'm pretty mechanical, as my Dad was a mechanic and I've rebuilt lots of things, but I'm not experienced working on boat motors.
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