DaveInGA
Well-known member
Motor: 1986 Mercury 75 HP Four cylinder Two cycle
It's been a while since I posted and I'm currently in the process of bringing my old motor back to life and getting my boat in the water for a shake out cruise. This motor sat for a good number of years before I bought it and while it doesn't appear to be worn out (compression is over 120 on all four cylinders) and I sprayed it with a two cycle oil/seafoam mix in each cylinder while I had it sitting for three years, I believe it's best with a motor to replace most "rubber" parts and possibly most of the electronic parts as well due to age/deterioration/damage.
The motor had a dirt dobber in the wiring and this caused the previous owner to fry the stator and all coil wiring coming from under the flywheel.
Here's what I've done to the motor so far:
1. Rebuilt water pump completely
2. Rebuilt Carburetors completely
3. Replace all fuel hoses inside the motor
4. Replaced the stator and trigger plate assembly
5. New fuel tank, lines, filters, bulb and fittings
What I haven't done or replaced:
1. Rebuilt fuel pump
2. Replaced spark plugs
3. Replaced spark plug wires
4. Replaced spark plug ignition coils (4 individual ones on this motor)
Went on a shake out cruise two days last week.
On the first day, the tachometer ground wire heat shrink split (oh what a feeling, chinola made heat shrink) and shorted the ground wire to the signal wire, so I couldn't check the propeller or motor for proper RPM range. The first day, the motor had excellent holeshot and solid acceleration, going fast enough to make me a little nervous, as it's been a while since I've been on a boat. Took the boat home feeling good and fixed the tachometer that night so I could finish shake out cruise the next day.
On the second day, the tachometer was working beautiful, but after the motor warmed up, it had operating problems above 2000-2500 RPM. The motor would shudder and wouldn't "get up and go." It felt like the motor either wasn't getting enough fuel or enough spark. A check of the fuel system hose confirmed good fuel feed to the motor with a tight bulb. The gas was new, bought near the lake and had the proper two cycle motor oil mix.
My initial inclination was to replace all the electric components that tended to go bad and to complete rebuild the fuel system, but my mechanic talked me out of it, which is why I have a list of items I haven't yet replaced.
After doing some research and some thinking, I'm inclined to go ahead and do the items on my "haven't done" list, then retest the motor. The cost to complete the items on the list is minimal and I wanted those done in the first place.
If I still have a problem when the motor warms up, I should choke the motor and see if the problem improves or gets worse. If it improves, I'll troubleshoot the fuel system. If it doesn't improve or gets worse, I'll troubleshoot the electronic ignition system further.
Anybody have any thoughts/suggestions?
It's been a while since I posted and I'm currently in the process of bringing my old motor back to life and getting my boat in the water for a shake out cruise. This motor sat for a good number of years before I bought it and while it doesn't appear to be worn out (compression is over 120 on all four cylinders) and I sprayed it with a two cycle oil/seafoam mix in each cylinder while I had it sitting for three years, I believe it's best with a motor to replace most "rubber" parts and possibly most of the electronic parts as well due to age/deterioration/damage.
The motor had a dirt dobber in the wiring and this caused the previous owner to fry the stator and all coil wiring coming from under the flywheel.
Here's what I've done to the motor so far:
1. Rebuilt water pump completely
2. Rebuilt Carburetors completely
3. Replace all fuel hoses inside the motor
4. Replaced the stator and trigger plate assembly
5. New fuel tank, lines, filters, bulb and fittings
What I haven't done or replaced:
1. Rebuilt fuel pump
2. Replaced spark plugs
3. Replaced spark plug wires
4. Replaced spark plug ignition coils (4 individual ones on this motor)
Went on a shake out cruise two days last week.
On the first day, the tachometer ground wire heat shrink split (oh what a feeling, chinola made heat shrink) and shorted the ground wire to the signal wire, so I couldn't check the propeller or motor for proper RPM range. The first day, the motor had excellent holeshot and solid acceleration, going fast enough to make me a little nervous, as it's been a while since I've been on a boat. Took the boat home feeling good and fixed the tachometer that night so I could finish shake out cruise the next day.
On the second day, the tachometer was working beautiful, but after the motor warmed up, it had operating problems above 2000-2500 RPM. The motor would shudder and wouldn't "get up and go." It felt like the motor either wasn't getting enough fuel or enough spark. A check of the fuel system hose confirmed good fuel feed to the motor with a tight bulb. The gas was new, bought near the lake and had the proper two cycle motor oil mix.
My initial inclination was to replace all the electric components that tended to go bad and to complete rebuild the fuel system, but my mechanic talked me out of it, which is why I have a list of items I haven't yet replaced.
After doing some research and some thinking, I'm inclined to go ahead and do the items on my "haven't done" list, then retest the motor. The cost to complete the items on the list is minimal and I wanted those done in the first place.
If I still have a problem when the motor warms up, I should choke the motor and see if the problem improves or gets worse. If it improves, I'll troubleshoot the fuel system. If it doesn't improve or gets worse, I'll troubleshoot the electronic ignition system further.
Anybody have any thoughts/suggestions?
