25hp merc losing power

[Steve R.]

I have 1998 25hp that is losing power after five min. Of full open and sometimes it dies but will start back up and go but not top speed. Starts out at 20mph and slows down to 10 or so.
Replaced fuel line and connectors but no change.
SR

 

[JB]

Re: 25hp merc losing power

I suspect that heat is the problem. Could be overheating, but It seem more likely that it is overheating something in the ignition system and dropping a cylinder.

You can try running it on muffs and heating up ignition parts with a hair dryer (NOT a heat gun). That might cause one cylinder to quit.

 

[Steve R.]

Re: 25hp merc losing power

I did check for spark when it was hot and both were fireing .
Do these little engines have a thermostat