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Member
(i apologize in advance for the novel, i'm trying to provide as much information as possible)
Hello,
I've been having issues this season with my 1996 75HP ELPTO 3cylinder Mercury 2-stroke (Serial No. 0G428168) in freshwater. I've owned my boat for ~6 years and haven't had issues in the past. This has been occurring consistently on numerous trips on the lake this entire season since it first touched the water for this year:
Background Information:
Current troubleshooting:
Thank you very much for any/all help! I'm not sure which way to go from here. Ideally, as everyone is aware of, throwing parts at it and hoping something sticks is not the way I want to go with this. I'd at least prefer to have a priority of what to consider first.
Hello,
I've been having issues this season with my 1996 75HP ELPTO 3cylinder Mercury 2-stroke (Serial No. 0G428168) in freshwater. I've owned my boat for ~6 years and haven't had issues in the past. This has been occurring consistently on numerous trips on the lake this entire season since it first touched the water for this year:
- OVERVIEW: boat runs 5-7mph slower (usually i get 37-40mph at 4800-5k rpm, now i'm stuck at 30-32mph at 4200rpm and trimming up further causes porpoising with no RPM gain)
- MISSING TOP-END RPM: motor doesn't reach max rpm at wide open throttle (4800-5k rpm is expected, but it tops out around 4200rpm and porpoises if i try to trim it up further to its normal running trim setting)
- NOTE: Sometimes, when i'm alone, i'll feel the motor gently surge forward around 4200rpm at WoT (like it WANTS to go) but once it smooths out if i trim it up slowly i can get it to spin up to its max running rpm of 4800-5k. When I add a passenger, this scenario happens maybe 1 in a 20 times and i most always cannot reach max rpm.
- SLIGHT RPM LOSS AT WOT: motor randomly hesitates while cruising at wide open throttle (me & passenger will be going 30mph/4200rpm at WoT and without touching the throttle or hitting any waves, the motor will drop RPMs and slow down to 27mph and eventually go back up to 30mph)
Background Information:
- STORAGE: carbs are fogged with fogging oil prior to winter storage
- STORAGE: fuel stabilizer is added to the gas tank prior to winter storage
- PROP: running the same prop (19p) for the entire time I've had the boat (6 years) and ive never had these running issues in the past
- BATTERY: Starter battery is ~5 years old, has a State of Charge of 12.4v which is ~75% (mentioning this incase it could cause an issue)
- WATER PUMP: Newly installed waterpump this spring before putting the boat in the water for the season
- THERMOSTAT: Newly installed thermostat this spring before putting the boat in the water for the season
- STEERING TAB/TRIM TAB: This was adjusted this spring to center out my steering (can't imagine this would cause an issue but still mentioning it)
- The boat sits in the water at a dock from spring until fall, so it's easy for me to take it out for a spin after modifying something
Current troubleshooting:
- PROP: inspected by a local prop shop and 1 small curve on 1 of the fins was found but he said at most i'd notice a 1-2mph loss and possible early cavitation but nothing major; he identified the hub in the prop is not spun
- PROP: tried spare prop in good condition (21p; usually run a 19p) and boat had same issue with early porpoising and not reaching max rpm
- FUEL: added seafoam to the gas tank (this actually fixed the issue when it first arose last fall, but has not made a difference yet this year after running a few cans through it and the carbs directly)
- FUEL FILTER: drained, inspected, installed new fuel filter and inlet/outlet fuel lines that connect directly to the filter
- PLUGS: after running the boat for a trip out, i will check the plugs and they do appear "wet"; i'm told this is common for how a 1996 Mercury 2stroke runs. Taking a lighter to it, it does not ignite the fluid on the end of the plug.
- TRIM: Sometimes when it's only me in the boat, it will reach max rpm at 37mph/4800rpm; i can trim the motor up to its max trim height before cavitation and the boat runs straight with no porpoising; BUT, always when i add a passenger, the boat porpoises when it reaches its (slower) top speed at 30mph/4200rpm when attempting to trim it up to its usual max trim height and will not get over this "hump"
- TRIM: (I haven't 100% confirmed this yet so maybe don't take it too seriously) there have been a select-few times where, when the boat would hit its stalling point at 4200rpm and porpoise early, I would make a slight and long left turn and this would seem to prevent the early porpoising when trying to trim it up further, which would actually allow me to trim the motor up and get it to spin to max rpm and then I can straighten the boat out and run it at top speed
- THROTTLE CABLE: inspected the throttle cable and it appears to be opening up all the way; manually moving it gives me the same amount of travel. i even had a friend try opening the throttle further (there was a little extra play) by hand while under power and no RPM gain was achieved.
- CARBS: All 3 carbs have been treated with carb rebuild kits, installed by a licensed mechanic
- HULL: Hull was inspected for any major buildup that could cause the issue, nothing stuck to the hull/no damage.
- RECTIFIER: Rectifier was burnt out; new rectifier installed as tachometer wasn't working initially; since installing this, the boat started being able to reach max rpm again with just me in the boat (before doing so, it consistently never reached max rpm with just me in the boat, it was stuck at 4200rpm; i don't know how a new rectifier could've changed the way the boat runs...; now i get the behavior as mentioned in the "NOTE:" above in the 2nd bullet point at the top of this post)
- I've heard a burnt out rectifier may cause a stator to go bad; can a bad stator cause a running issue like this?
Thank you very much for any/all help! I'm not sure which way to go from here. Ideally, as everyone is aware of, throwing parts at it and hoping something sticks is not the way I want to go with this. I'd at least prefer to have a priority of what to consider first.