Loss of Power at full throttle

[benchwarrant]

Senario: While traveling at full speed my 25 hp, 2 stroke merc. will briefly lose power for a second every 50 or so yards. The gas is fresh. The motor starts fine and at slower speeds I do not have this problem. It is almost like at full demand, it is not getting all the gas it needs. I checked the fuel filter in the 6 gal. tank (o.k). I could not get the fuel filter under hood off. (on too tight) but it did not appear to have any debris inside. The gas looked good. No kinks in the line. The spark plugs are at least 3 years old but did not appear to be too fouled. (I put new ones in).
I am thinking either the fuel filter is plugged (It probably has never been changed) or regretfully the fuel pump ($$$ ouch).
I am not a mechanic. Any thoughts or ideas would be greatly appreciated. I should note the the water temp was 34 Deg. with an outside temp of 36 deg. (but I have ran the motor in the past in cold temps with no problems.
Thanks in advance
-Benchwarrant

[Hotwired]

My guess is an intermittent bad coil.
You are dropping from 2 to 1 cylinder when the coil heats up.
My 30hp Evinrude did the same thing.

[TONGA]

Hotwired my indeed be correct but it could also be a switchbox if it has one, when you said “but it did not appear to have any debris inside” makes me think it has a glass bowl on it and it would probably have points! It could still be a coil.
So please tell us the make and year of the motor so we can determine what kind of ignition you have then we can tell you how to trouble shoot it!
If you don’t know the year give us the model and serial numbers and we can figure that for you also

[benchwarrant]

2002 Mercury 25 hp (long shaft) 2 stroke.

I don't have Ser. or Mod. # off hand

Thanks!

[bassdisaster]

Could simply be a clogged carb problem, run some Mercury Quicksilver Quick kleen thru it, see if after a few gallons the problem goes away, if its not carb's it has to be ignition!
Good luck

BD

[ENCORE]

BEFORE, you spend a ton of money, do yourself one last thing. Change the fuel line!
Fuel lines can be a major problem and the problem really shows its ugly head when you throttle up or, at full throttle. Two things can be happening, One: the fuel line is leaking air some place. Two: the fuel line can be collapsing. This is probably one of the most common problems that you can have, if you know you have good fuel.
The wife and I bought a NEW 30' that we slipped at Toledo Beach Marina. We went out to fish one day and got just outside the channel and I put both throttles down. It worked just fine, until it got to plane. Then one engine wanted to quit. It would run ok at idle and just above, but wouldn't run wot. Anyway, dealer paid for a guy to come down and install a new fuel pump. We took it out and the same thing. Came back in, he put an electric pump that he had on it and checked the line. THERE IT WAS... !!! Brand new boat and the fuel lines were bad. Seems that the manufacturer had a recall (Gates I think) and the boat manufacturer decided to just see how many problems he might have.
Replace the complete fuel line.

[tdejong302]

Had the same problem last summer. After replacing lines, putting on new seals, new water seperator had the carb cleaned. That was the problem. Try some seafoam first if that doesn't fix it. Have your carbs cleaned.

Also heard the fuel pump diagrahm can cause this. Good luck.

[1mainiac]

My boat had a similar problem this year after having the entire fuel system gone thru several times found bad plug wires. They were installed new prior to buying the boat this spring and looked perfect so thought it had to be fuel cause it would only mess up at WOT. Sure am glad the dealer I bought it from Halls in Muskegon stood behind it all summer till we got the bugs out most places would just say sorry cause it was a used boat. They easily had close to a grand in labor chasing the problem down and thought it was fixed several times. The day we found the problem one of their techs loaded up tools and parts and we hit the lake for several hours till he found the problem changed wires and plugs on the water and ran like a Swiss watch the rest of the summer.

[Topshelf]

My guess is an intermittent bad coil.
You are dropping from 2 to 1 cylinder when the coil heats up.
My 30hp Evinrude did the same thing.

What he said :yeahthat: