Hello,
I can get the precise manufacturer model number if required, but the engine I’m having issues with is a 2007 25HP Mercury EFI Four-Stroke outboard with hand tiller. It is an electric start engine (external marine battery) and has hydraulic trim via an electric up/down switch on the hand tiller. It is still in very good/new condition with only a few hours of use per year. I am the original owner.
Now, to the issue. I have had very few problems with this engine. A couple years ago Mercury replaced a part in the fuel intake area due to a defect that was starving the engine of fuel. This problem was quite obvious because the engine would not even start and if it did it would only run for a couple of minutes maximum. Since that repair was done it has been running like new again.
This season, however, I’m having a similar yet what I believe to be unrelated issue. It ran fine for the month of May. The past week or two, however, I have issues when revving up the throttle between 80-100%. The engine runs fine at idle and up to about 80% throttle, including on plane. However, once I increase to above 80% on the throttle, after running fine at this for about five minutes or so, the engine begins to wildly rev up and down. After about five minutes above 80% it will suddenly rev down, as if the fuel is cut off, yet as quickly as it did that it revs back up. It starts repeatedly doing this so that I’m thrown about with the constant decrease/increase of speed that ensues. Pumping the primer bulb while this is occurring has no effect. If I cut the throttle back to below 80%, it levels out and runs perfectly fine again.
I am getting no warning lights or beeps to indicate low oil, rpm too high, engine overheating, etc. Manual oil level check is fine. Fuel is getting through without issue as when I take the cover off the outboard I can literally see the fuel flowing through and in addition my gas tank level decreases with use.
Carbs are also fine. I was wondering if maybe it is gear oil but at the end of April I had drained and filled it so that seems unlikely as well.
The motor is only used in freshwater on Georgian Bay (Lake Huron). Prop size not an issue as it’s the same I’ve always used.
Does anyone know what this issue may be? I don’t frequently run at open throttle, but I’d like to be able to when needed and have never had this issue before. If possible I am trying to avoid a steep mechanic bill if this is something I can resolve on my own.
Any feedback or suggestions are greatly appreciated!
Cheers
Edit: For what it’s worth, I do not believe it to be any form of ethanol poisoning as I only use high octane, ethanol-free marine fuel from Petro-Canada via my local marina (94 Octane Ultra Premium) and do not store it for more than two weeks at a time.
I can get the precise manufacturer model number if required, but the engine I’m having issues with is a 2007 25HP Mercury EFI Four-Stroke outboard with hand tiller. It is an electric start engine (external marine battery) and has hydraulic trim via an electric up/down switch on the hand tiller. It is still in very good/new condition with only a few hours of use per year. I am the original owner.
Now, to the issue. I have had very few problems with this engine. A couple years ago Mercury replaced a part in the fuel intake area due to a defect that was starving the engine of fuel. This problem was quite obvious because the engine would not even start and if it did it would only run for a couple of minutes maximum. Since that repair was done it has been running like new again.
This season, however, I’m having a similar yet what I believe to be unrelated issue. It ran fine for the month of May. The past week or two, however, I have issues when revving up the throttle between 80-100%. The engine runs fine at idle and up to about 80% throttle, including on plane. However, once I increase to above 80% on the throttle, after running fine at this for about five minutes or so, the engine begins to wildly rev up and down. After about five minutes above 80% it will suddenly rev down, as if the fuel is cut off, yet as quickly as it did that it revs back up. It starts repeatedly doing this so that I’m thrown about with the constant decrease/increase of speed that ensues. Pumping the primer bulb while this is occurring has no effect. If I cut the throttle back to below 80%, it levels out and runs perfectly fine again.
I am getting no warning lights or beeps to indicate low oil, rpm too high, engine overheating, etc. Manual oil level check is fine. Fuel is getting through without issue as when I take the cover off the outboard I can literally see the fuel flowing through and in addition my gas tank level decreases with use.
Carbs are also fine. I was wondering if maybe it is gear oil but at the end of April I had drained and filled it so that seems unlikely as well.
The motor is only used in freshwater on Georgian Bay (Lake Huron). Prop size not an issue as it’s the same I’ve always used.
Does anyone know what this issue may be? I don’t frequently run at open throttle, but I’d like to be able to when needed and have never had this issue before. If possible I am trying to avoid a steep mechanic bill if this is something I can resolve on my own.
Any feedback or suggestions are greatly appreciated!
Cheers
Edit: For what it’s worth, I do not believe it to be any form of ethanol poisoning as I only use high octane, ethanol-free marine fuel from Petro-Canada via my local marina (94 Octane Ultra Premium) and do not store it for more than two weeks at a time.
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