mercury 25hp 2006

i have a 2006 mercury 25hp 4 stroke efi and when i connect the earmuffs it idles and runs perfect but when under a load in the water then i will only go about 8mph at 4100rpm. why is it doing this and the boat is a 2007 lowe stinger 160. please help!

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Jun 10, 2021
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starstarstarstarstar 		Results on 07 Merc 25hp
by: Alex Garabedian

I ended up having to replace the whole fuel system, every piece it was full of separated oil deposits from bad fuel. Then I had to go through prop selection, and then i added a water separation filter between the tank and the engine. Runs great now. Was not cheap by any means. In spoeaking to two mechanics this is usually the problem with theses engines
Jun 10, 2021
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starstarstarstarstar 		Running too lean
by: Anonymous

My 1983 80 hp merc did the same thing. Took me months to figure it out. When it is in the water there is a lot more back pressure against the exhaust so the driveway adjustment isn't rich enough for the water. Put the boat in the water, have someone drive it to the speed where it stops revving. Turn the mixture screws about 1/8 turn at a time and it should fix the issue. There was never any mention of this in the Seloc manual. I stumbled onto it out of desperation while my son was at the helm. Good luck.
Jun 01, 2021
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starstarstarstarstar 		2006 Mercury 25hp 4 stroke EFI
by: John Carillon

This engine has been hard to start from the day it was new. It seems as though there is no compression release. Electric start goes with a new fully charged high capacity battery goes bump bump bump each time the ignition key is switched on. It wil finally start and run smoothly. Impossible to mechanically pull start. Strarts right up if started agiain within an hour after shut down. Why? What’s amiss?
Aug 12, 2020
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starstarstarstarstar 		Same issue
by: Al

I'm having the same issue with my 2011 9.9hp. Revs up no problem in neutral, put in gear and only get like half throttle and 8mph Not enough to get fully on plane on a little 14ft starcraft alum boat.
Apr 05, 2020
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starstarstarstarstar 		Having same issue but
by: Alex Garabedian

Having same issue on a 2007 but it does not seem to even get 1500rpms when WOT under load but will scream when in neutral
Did you find out what is the issue?

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