Engine issues 25 hp

[ghs53089]

I have a 97 mercury 25hp outboard thats runs perfect up to half throttle, but from half to full throttle there is no power. After sitting at full throttle it will gradually speed up and run normal after 30 secs to a min. Ive had the carb rebuilt, new flywheel and magnets, all ignition parts check ok, and compression is good. ANY IDEAS?? Thanks

 

[hamit59]

Re: Engine issues 25 hp

It sound like you starving for fuel. You said the carb was rebuild but was it cleaned. I wish I could count how many REBUILT carbs. I have had in the shop. I have found that so many guys can put gaskets in and a needle and seat. in a carb and say it was rebuilt in truth it was. The thing they needed to do most was just clean the low speed jet and the high speed jet.You can do this by soaking or by pick cleaning with torch tip cleaner I use both.

I will say you need to look at the fuel system as a whole tank, lines primer, connector, filters(if any) fuel pump and last but not least the carbs.

I always do a full check spark and compression and drop cylinder to find out the condition of the motor then. I go into fuel system. Some many times it not the carbs in fuel starving. It's the fuel pump a small hole in the diapham will cause the problem. You can check it while running pump the primer it if picks up then you'll know you need to rebuild your fuel pump, fuel pump parts are so cheap I would put a kit into it.
Keep us posted with what you find

 

[ghs53089]

Re: Engine issues 25 hp

When the carb was rebuilt it was cleaned and the fuel pump was rebuilt. When that didnt solve my problem i got a new fuel tank and line.

 

[ghs53089]

Re: Engine issues 25 hp

today i replaced the fuel lines to the fuel filter and from the filter to the carb and ran seafoam through the fuel system. It seemed to do the job as the motor was running much smoother

 

[hamit59]

Re: Engine issues 25 hp

Hi,
I glad your on your way to finding the cause.I still think you need to look at your carb. I would hate for you to come back here asking how to rebuild a 25 hp.I still think you have a lean run condition at high speed sea foam is some good stuff .I use it all the time to decard a motor and even if you do get it running better with the seafoam there still a chance you'll not get enough fuel to oil the motor. You never said how many hours were on your motor.

The first thing I was told in tech school listen to the owner.
Happy boating