Merc 150 ('85??) power loss

[RLeeDude]

I was motoring along at about 55mph and suddenly the motor began to cut out and bog down. It remained running and ended up at a max of about 20 mph. I headed for the dock and about 15 minutes at this speed it began to slowly pick up RPM's I adjusted the trim and ended up at about 40mph. It would "miss" sporadically, but I made it back. When I reached the dock I noticed it seemed like the exhaust was much "richer" than usual.
I recently had it tuned including a fuel filter, but I can't help but think that's what it sounds like...
Any thoughts???
Thanks

 

[Laddies]

Re: Merc 150 ('85??) power loss

Try cking. the engine for spark, that could be a switch box or part of the stator failing

 

[RLeeDude]

Re: Merc 150 ('85??) power loss

Laddies,
I drained the old fuel (that had been in it almost 3 years) and replaced the fuel filter. This is also the same boat I rewired and replaced gauges, and ignition on. This power loss problem occured prior to the rewire. Anyway I fired her up (in neutral) at home and she ran like a champ got up to about 5500rpms with more to go. Went to the lake today... she fired right up again, revved nicely in neutral, but when I engaged the prop I could only get up to about 1800rpms WOT. Ran like that (seemed to be missing) for several minutes then planed out and got up to 3600rpms (still WOT). I fished for a few hours then went to motor elsewhere and could only get the 1800rpms. Stopped for another few hours headed to ramp at 1800 and about 5 minutes into that got up to 3500rpms. Top speed reached today was about 37mph, prior to the problem I could get about 57mph.
I'm baffled.
If you still think this could be the stator or switch box is there any way I can test them at home or do I need to take it to a mechanic?
Otherwise any other thoughts.

Thanks, Rick

 

[j_martin]

Re: Merc 150 ('85??) power loss

At 5500 rpm with no load, the pistons are trying to change holes. You might have broken something.

Start with a compression check, then spark, and so forth.

John

 

[studlymandingo]

Re: Merc 150 ('85??) power loss

If you a DVA meter and a manual, you can check the stator and the switchboxes. Have you done a spark check with a gap-tester?​

 

[RLeeDude]

Re: Merc 150 ('85??) power loss

I checked spark today and all 6 are firing. I also did some resistance checks (based on some info I got off the "CDI" website) on a few stator wires. They checked out fine. I don't have a DVA so it sounds like I need to round one up to check out the stator and switch boxes. Will I need a manual (I can't locate mine) to get test data or can I get that online? Also what is the best way to keep the flywheel from turning so it can be removed?

 

[studlymandingo]

Re: Merc 150 ('85??) power loss

You will need a DVA meter in order to properly check the stator. How did you test the spark? If you used a spark-gap tester, did you have a consistent and strong blue spark on all cylinders?

Some people use an inductive timing light hooked to each plug wire successively while at operating speed on the water (never run your outboard above idle on the muffs at home) this can tell you if you are experiencing a high speed miss.

Have you tested compression on the motor?​

 

[StriperLover]

Re: Merc 150 ('85??) power loss

not trying to hi jack this thread but really why is it that everyone says dont go over idle on the muffs at home? every motor in everything else has no problem revving up in neutral with no ill effect why are boat motors so different? i understand not to over rev but why not like up to 5K?