'94 25 hp losing power when warm

[ChipnKim]

I bought this boat in July with a '94 Johnson 25 hp. First day out boat ran great for about 1/2 hour then started to bog/sputter. Backed off to 1/2 throttle ran fine. I suspected coils but Local dealer said power pack is more likely. Changed it. Next time on the water, the same thing. Brought it home and tested water flow (in case of over heating) and decided to change water pump assembly. Out on lake last week and still lost power/ bogged down about 30 mins at 90% throttle. Only this time, it stalled after backing off throttle. Started right back up and ran fine at 40% throttle. This week, changed out fuel to ethonol free fuel. On lake today problem is getting worse. Runs great for about 30 mins. Only this time i was barely able to run 20% throttle to get back to dock. I really do not think its fuel related, and will replace coils this week. Anyone had similar issue and know the secret?

 

[interalian]

Sounds like it's starving for fuel to me. Next time it does that, try squeezing the primer bulb and see if it picks up again.

 

[ChipnKim]

Did that. No change. That is why i think its coils. I thought maybe, just maybe, it could be fuel pump since it seems to only occur after about 30 minutes of 90% throttle, but since it had started stalling, it fires up immediately.

 

[ondarvr]

It won't make any difference if you run E10 or E0.

Coils typically go bad before a power pack.

Fuel problems normally result in slower and smoother surging or loss of RPM's, electrical problems tend to react quickly, like flipping a switch. Which is it?

 

[ChipnKim]

Progressive. Motor will begin to miss, then lose power like spark is shut off momentarily. I drop to half throttle, and it had run fine. However, today was the worst it has been. The half throttle worked ok for a while, then lose power and surge, then off, then surge slightly, then almost stall. Drop back to near idle and fine again. But, can only get underway with less and less throttle. Was barley 20% throttle to get back to dock.

 

[racerone]

Compression test done ??

 

[ChipnKim]

I'm going to do a few diagnostic tests today. I'll post results. It seems this is not an uncommon issue with Johnson/Evinrudes. I just didn't see any likely culprits from past postings.

 

[racerone]

Hook up a timing light an observe the performance of the ignition system / coils.------both cylinders from idle to full throttle.