1994 Evinrude 150hp - Stumble at WOT ( with video link)

[throbbingrod]

Hi everyone, finally got the boat back together and took it out this weekend. It cruises great at 1/2 Throttle (~4000 RPM) but when I open it up to wide open, it will shortly give me a constant alarm and stumble hard. If I return to idle, the alarm will quit shortly but the miss and stumble did not. This motor does seem to crank really hard, but I don't know if that is related. When it was running like this last night, I tried pumping the primer bulb and that was still hard and had no change.

I guess I'm going to start with fresh plugs, fuel filter but not sure where to take it from there.

 

[racerone]

It sounds horrible.----Not running on all cylinders.-----Compression test first.----Then check for spark on all 6 leads.----Good spark will jump a gap of 3/8" or more.-------Model # is ?----Sure it is a 1994 model ?

 

[Bosunsmate]

Id check timing too, maybe a powerpack going out.
How do spark plug combustion colours look?

 

[throbbingrod]

Ok, so here's an update. After digging around online, I've determined that the motor is kicking itself into SLOW mode.

First I looked up the model # and the actual year and the motor is a 1990.

I checked all the plugs and they looked OK, but I changed them anyway ( now I have spares). All had good oil on them, not too much, but not dry and white. Compression looked OK, 70-85 on all holes which looked to be in spec for this motor. I only panicked a little before I looked it up thinking it was supposed to be up around 120.

I took the family out yesterday for another test run. It cruised perfectly! I was able to pull kids around on the tube all afternoon and ran between 3000-4000 RPMs without any issue. At the end of the day, I tried to duplicate my issue and couldn't get it to go into SLOW mode. At WOT it looked like the RPMs were ~ 5200.

So, in the end, I'm not sure if new spark plugs fixed my problem, or it was just an intermittent problem that will show its self again. Possibly I had less weight on board when the problem was happening and maybe was over -revving the motor? Maybe I need to tell the wife I need a different prop.... I think I have a 15x17 on there now.

 

[throbbingrod]

PS, everyone says their VRO alarm does a 1/2 second beep with the key coming on. Mine will do a constant quick beep, beep, beep until the motor is running. Then the alarm goes off.