Late 90's M140A2 RPM Drop = Power Loss

TheDerby

Cadet
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Dec 6, 2010
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During normal operation engine runs fine. 20 min later RPM drops to 2200ish. No response to throttle position unless lower then 2200.

Putter, putter then pick back up but ultimately drops again and back to the ramp I go slowly.

Compression: 120 on all but bottom at 115(always has been for last 8 years)
Spark: 7/16" and strong.
Fuel: Bulb pressurized, filters new, fittings new, pump new, tank new.

Here is the thing, I had water in the tank. Boat still ran like a top but I stopped and replaced the tank before running again.

All symptoms after restart with new fuel everything up to carbs. There is an appearance of unburnt fuel from exhaust.

Plan is to rebuild carbs, sync/timing, test limp-mode senders, temp, pressure and oil level....but what else?

New plugs look same but not dry.

Salt water boat.

I just dont want to miss something while I have everything apart.

Yes, I have and use the manual.
 

pvanv

Admiral
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Apr 20, 2008
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6,500
Could be almost anything, but typically fuel is the first thing to check. Could be a bit o crud in one carb. After that and after syncing timing, if problems persist, verify resistance of all ignition components. Could be a thermally-acting-up ignition issue.
 

TheDerby

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Dec 6, 2010
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Could be a thermally-acting-up ignition issue.

That and the frequency is what I am worried about.

Not fuel, just a coincidence issue and having to test out on the ocean.

California, no 2-strokes in the lakes around here.
 

TheDerby

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Dec 6, 2010
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Tested temp, pressure and oil lever senders....they work....or at least sound the buzzer which did not happen during power loss.

Carbs off and rebuilt. Some salt and grit, but not much. Hope that was it.

The manual does not explain how to set float level clearly. Just tweek the metal clip.

For the life of me, I cant figure out how bending clip is going to raise float without limiting the needle from seating properly. I ended up bending the plastic tab on two of the carbs. Floats are per spec now. Hope that works

Please advise.

Installing tomorrow morning PST.

I also plan on doing all ignition tests possible off or at idle. I dont have a tank and the ocean is an hour away.
 

pvanv

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Apr 20, 2008
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As with all outboard carbs, the floats should be parallel to the casting when the casting is held inverted.
 

TheDerby

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Dec 6, 2010
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As with all outboard carbs, the floats should be parallel to the casting when the casting is held inverted.


Not according to my service manual. They want the end opposite pivot to be 19.5mm above cast edge. That makes the float roughly 10degrees.

Please dont keep saying "All" you confuse a lot of people.
 
Last edited:

pvanv

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Apr 20, 2008
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I see that. I would consider that a bit low. Regardless, as long as it isn't way low, it should be OK. These are relatively forgiving carbs.
 

TheDerby

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Dec 6, 2010
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It was the carbs.

Boat runs better then ever.

However, in doing the sync/timing I realized that the carbs can never go WOT due to the Timing/Throttle cam. The cam can not be pulled far enough to get past 85% full open. Even if you shorten the throttle linkage to pull the cam further, the mechanism is at it's limit. There is no more leverage for the throttle linkage to pull the cam.

Wonder if that is by design? Should I expect 100% WOT at the carbs? I would like to think so

All work performed by the book.
 

pvanv

Admiral
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Apr 20, 2008
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Sounds like you are setup as a 120. The 140 should open all the way. Still, it should work OK at 85% open.
 

TheDerby

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Dec 6, 2010
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I am familiar with the 120/140 setup. Unless they provide a different cam profile, I am set per 140 guidelines.

The stops are not limiting cam travel. The cam itself cannot be pulled any further by throttle linkage even with it disconnected from main link. I'll try and post a picture.
 
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