# 25 HP Merc 4 stroke won't rev under load



## Captain Tan Can (Nov 9, 2005)

My 2000 Merc "Bigfoot" kicker after sitting since October 2008 was running poorly when I fired it up in the driveway. Stalled when I tried to accelerate, acted like only one cylinder firing for a while etc. It runs off the onboard fuel tank which had Stabil in it so I mixed some fresh gas and added Gumout carb cleaner in the 3 gallon tank that came with the motor and ran it off and on for a couple of hours in the driveway. Each time I shut it off and restarted after an hour or so it seemed to get better, would go WOT and idle OK. Went trolling last Friday and it ran great at slow speed for 3 hours. When I tried to accelerate it would only respond up to 1/2 throttle and when I pushed the throttle farther down there was no change in speed. If I went back to neutral it would rev up but not under load. It would only push my boat at 4.5 MPH and it will usually get up to around 8MPH. Runs smooth but no power. Its almost like a retarded timing problem in a car. Any suggestions ?


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## ENCORE (Sep 19, 2005)

Captain Tan Can said:


> My 2000 Merc "Bigfoot" kicker after sitting since October 2008 was running poorly when I fired it up in the driveway. Stalled when I tried to accelerate, acted like only one cylinder firing for a while etc. It runs off the onboard fuel tank which had Stabil in it so I mixed some fresh gas and added Gumout carb cleaner in the 3 gallon tank that came with the motor and ran it off and on for a couple of hours in the driveway. Each time I shut it off and restarted after an hour or so it seemed to get better, would go WOT and idle OK. Went trolling last Friday and it ran great at slow speed for 3 hours. When I tried to accelerate it would only respond up to 1/2 throttle and when I pushed the throttle farther down there was no change in speed. If I went back to neutral it would rev up but not under load. It would only push my boat at 4.5 MPH and it will usually get up to around 8MPH. Runs smooth but no power. Its almost like a retarded timing problem in a car. Any suggestions ?


New plugs? Use SeaFoam also. Probably don't have to tell you this but, gas now days sucks and goes bad quickly. Have you checked the fuel line for leaks and/or is there the possibility that it is collasping?
My 9.9 was running bad and hasn't ran right since new. Took it back to the dealer this spring and the carb was removed. Somehow... that carb was full of junk. They cleaned it completely and it runs perfect AND starts properly now. However, they questioned my fuel, as it looked really bad. The boat was filled with premimum last fall from a 1/4 full.
Somehow it always boils down to fuel or fuel lines...
Good luck with it.


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## Quack Wacker (Dec 20, 2006)

I had a similar problem with my motor and it turned out to be a gummed up fuel filter, not saying that is what is wrong with yours, but worth a shot. Cheap fix too.


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## Captain Tan Can (Nov 9, 2005)

Thanks guys, I also thought it may be fuel related ie plugged secondary jets etc. Thats why I ran the Gumout through it. I believed it helped with the starting and idle but I may have to go further by changing the fuel filter and possibly rebuilding the carb. What made me think that is was something else was the fact that it ran great while trolling and was also smooth when running at half throttle.


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## sfw1960 (Apr 7, 2002)

I have an '02 25HP MerC.
The fuel pickup tube* IN* the tank where it attaches to the coupler had broken loose (super glued on) and was sucking air - you might check there...
(I had ran the motor with 'muffs' and pulled the assembly up out of the tank while running and could visibly see the bubbles being pulled in the tube.)

I re-applied super glue & put cable ties around the tube and haven't had a problem since...


G'Luck!!

Robert


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## Damark Marine (Mar 26, 2008)

I think I would agree with everyone here, fuel related problems seem to be the most common problems we see. It seems that carb work may be in your future.

Jeff


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