I've been on quite the journey with this motor. It's a 1995 Mercury 75HP ELPTO 2-Stroke outboard motor. Heres the jist... This motor shakes, smokes, and dies periotically at idle. Fast forward to the last paragraph to see a short version of all the maintenance that has already been done. Heres the history...
2023:
I bought a boat with this motor attached. I was told that the original owner swapped motors with his other boat, so this is not the original motor. Before swapping, the motor was overheated. After a visit to the shop, a mechanic deemed the engine still good. When I went to check out the boat, we started the motor in the driveway on muffs and it started up first try. Now that I own the boat, I have checked a few things due to the motor running rough at idle and excessive smoke. Due to the overheating event, I checked compression. It checked out good. I can't remember the exact values, but they were all within 10psi of each other and above 100psi. I then rebuilt the carbs. Cleaned and new gaskets. I set the idle to 750rpm and Idle in forward gear to 650RPM per the manual. No help. Still running rough at idle. Runs good at WOT.
2024:
I change the fuel filter and timed the engine according to the manual I found online. The filter seemed to be clean, but i had an extra sitting around. The manual used said to time the idle to 2ATDC - 6BTDC and Max timing to 20BTDC. I think i set the Idle to 2BTDC. No help. In fact, it runs worse in my opinion, but still runs okay at WOT. I used a spark plug tester and I'm getting power to all spark plugs. I have also synched the oil pump so that the lines align in accordance to the manual.
2025:
I bite the bullet and send it to the mechanic. I tell them my story and they say that they are going to rebuild the carbs again. When I get it back I find an oil leak and it still doesn't run any better. I brought it back to the mechanic and they said they did not like the carb kits they put in, so they replaced the kits with OEM carb kits. They prove that it runs well on muffs and send me on my way. At this point it seems to run a little better and smoke a whole lot less. Things are looking up right? Not really. I took it out on the water and it seemed like I wasn't able to get full power out of the engine and it seemed like the idle was set to low. So stupidly I looked at timing again. The timing was off by a couple degrees. I adjusted the idle speed screw and idle timing again. I did not touch max timing hoping it would be ok as it seems to run well at WOT. While messing with all of that I noticed that the mechanic did not tighten the throttle arm connected to the carbs, so that explained my power issue. It still didn't run great on the muffs, so I changed the spark plugs out. It ran pretty darn good on the muffs after that. I took it out again and now I cannot get any power out of it. If I pump the bulb for a little bit I would get a few seconds of power, so I suspected fuel. I took apart the fuel pump and found the diaphragm cracked and worn. I put a new fuel pump kit in and new fuel filter. Now I got power back, but it hardly stays running at idle. I notice that it runs smooth when I choke it. By choke it I mean I press the button on the throttle and rev the engine up. It runs smoothly up until I put it into gear and it will run for few seconds and die. If I pop it in gear quick enough and rev it up past 1000RPM, It will stay running and run okay at WOT.
Currently this is how it sits. Just this week, I ran a multimeter across the ignition coils. I got .02 Ohms across both posts and about 950 Ohms from the posts to where the ignition cables enter the coil. From what I can tell, this all checks good. I found a CDI troubleshooting guide for my model ignition components (p/n: 134-9021-3) and tested the stator and trigger resistance. Both checked out good. I added a reference to the link below for the values. I'm thinking about going out to buy a spark gap tester to confirm I am getting a strong enough spark and running another compression test. Could maybe be the switchbox? I am also thinking of rebuilding the carbs a 4th time. Seems excessive, but possible part of the fuel pump got lodged up there. Any thought on where to go from here.
Maintenance Summery:
- Compression Test (Good)
- Carb Rebuild (X3)
- Idle adjustment (To many times to count)
- Oil pump synch
- Fuel Filter (X2)
- Tested Spark (Good)
- Adjusted Timing (X2)
- Rebuilt Fuel Pump
- Checked Coil Resistance (Good)
- Checked Stator Resistance (Good)
- Checked Trigger Resistance (Good)
CDI Troubleshooting Guide:
2023:
I bought a boat with this motor attached. I was told that the original owner swapped motors with his other boat, so this is not the original motor. Before swapping, the motor was overheated. After a visit to the shop, a mechanic deemed the engine still good. When I went to check out the boat, we started the motor in the driveway on muffs and it started up first try. Now that I own the boat, I have checked a few things due to the motor running rough at idle and excessive smoke. Due to the overheating event, I checked compression. It checked out good. I can't remember the exact values, but they were all within 10psi of each other and above 100psi. I then rebuilt the carbs. Cleaned and new gaskets. I set the idle to 750rpm and Idle in forward gear to 650RPM per the manual. No help. Still running rough at idle. Runs good at WOT.
2024:
I change the fuel filter and timed the engine according to the manual I found online. The filter seemed to be clean, but i had an extra sitting around. The manual used said to time the idle to 2ATDC - 6BTDC and Max timing to 20BTDC. I think i set the Idle to 2BTDC. No help. In fact, it runs worse in my opinion, but still runs okay at WOT. I used a spark plug tester and I'm getting power to all spark plugs. I have also synched the oil pump so that the lines align in accordance to the manual.
2025:
I bite the bullet and send it to the mechanic. I tell them my story and they say that they are going to rebuild the carbs again. When I get it back I find an oil leak and it still doesn't run any better. I brought it back to the mechanic and they said they did not like the carb kits they put in, so they replaced the kits with OEM carb kits. They prove that it runs well on muffs and send me on my way. At this point it seems to run a little better and smoke a whole lot less. Things are looking up right? Not really. I took it out on the water and it seemed like I wasn't able to get full power out of the engine and it seemed like the idle was set to low. So stupidly I looked at timing again. The timing was off by a couple degrees. I adjusted the idle speed screw and idle timing again. I did not touch max timing hoping it would be ok as it seems to run well at WOT. While messing with all of that I noticed that the mechanic did not tighten the throttle arm connected to the carbs, so that explained my power issue. It still didn't run great on the muffs, so I changed the spark plugs out. It ran pretty darn good on the muffs after that. I took it out again and now I cannot get any power out of it. If I pump the bulb for a little bit I would get a few seconds of power, so I suspected fuel. I took apart the fuel pump and found the diaphragm cracked and worn. I put a new fuel pump kit in and new fuel filter. Now I got power back, but it hardly stays running at idle. I notice that it runs smooth when I choke it. By choke it I mean I press the button on the throttle and rev the engine up. It runs smoothly up until I put it into gear and it will run for few seconds and die. If I pop it in gear quick enough and rev it up past 1000RPM, It will stay running and run okay at WOT.
Currently this is how it sits. Just this week, I ran a multimeter across the ignition coils. I got .02 Ohms across both posts and about 950 Ohms from the posts to where the ignition cables enter the coil. From what I can tell, this all checks good. I found a CDI troubleshooting guide for my model ignition components (p/n: 134-9021-3) and tested the stator and trigger resistance. Both checked out good. I added a reference to the link below for the values. I'm thinking about going out to buy a spark gap tester to confirm I am getting a strong enough spark and running another compression test. Could maybe be the switchbox? I am also thinking of rebuilding the carbs a 4th time. Seems excessive, but possible part of the fuel pump got lodged up there. Any thought on where to go from here.
Maintenance Summery:
- Compression Test (Good)
- Carb Rebuild (X3)
- Idle adjustment (To many times to count)
- Oil pump synch
- Fuel Filter (X2)
- Tested Spark (Good)
- Adjusted Timing (X2)
- Rebuilt Fuel Pump
- Checked Coil Resistance (Good)
- Checked Stator Resistance (Good)
- Checked Trigger Resistance (Good)
CDI Troubleshooting Guide:
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