135 HP lacking power

hawk816 · Dec 6, 2003

The question:- I have a 135 HP "Black Max" series Mercury engine S/N:- A981123 (1986/87 Yr Model) which is lacking power. Symptoms:- max attainable RPM is 3000 - 3500. I have had numerous mechanics try to sort out the problem, I have had coils, plugs, compressions packs & all carbys checked with all checks showing it is ok. The motor starts and runs well on idle and low RPM, however when I advance the throttle it will not go past the above stated RPM range. Can this be "high speed stator problems"? If so how do I check, service manual does not show these details plainly enough, any thing I should be aware of?

AndyL · Dec 7, 2003

Re: 135 HP lacking power

I think you may be on the right track however I would check all throttle and advance linkages. Check also the that the fuel line is not restricted. Check to see if the primer bulb stays firm at all rev ranges and is not collapsed. I assume you have replaced the fuel pump and that it is assembled correctly. Does the throttle lever at the engine end move full travel. I don't know what the correct test procedure is for the stator or switchboxes but you are definetly in the right forum for tech stuff like that. Andy

DJ · Dec 7, 2003

Re: 135 HP lacking power

hawk816, Do the easy stuff first. 1. Check the linkages, as mentioned-good tip. 2. Run the engine with a seperate six gallon tank and a different fuel hose. 3. Check the O'rings on the male and female fuel attachments.

bluebyyou · Dec 7, 2003

Re: 135 HP lacking power

I once had a similar problem and it turned out to be my metal gas tank kept fouling my carbs due to rust on the bottom (even though I'd just had the carbs rebuilt). I'd check resrticted linages and fuel. Since I had that fuel problem the mechanic put a clear in-line fuel filter on between the ball and the engine so I can always make sure fuel is flowing and doesn't have a lot of crud in it.

hawk816 · Dec 7, 2003

Re: 135 HP lacking power

Thanks for all the tips, will give it a go. The carbs were cleaned and checked during the troubleshooting exercise, no problems found. What was found is that when the engine was loaded (3000 RPM) No 2 cyl lead off/on there appeared to be no engine RPM change. All other cylinders checked with a definite RPM drop noticed. Further check of No 2 cylinder spark showed that there was in fact spark from lead to plug end. Compressions tested OK, Borescope inspection of No 2 cylinder indicated no visable problems. Will try another tank. (Tank currently fitted is SSteel with a water separator, fuel pump overhauled 4 months ago new filters fitted). Could this problem be caused by a hole in fuel pump diaphragm?

AndrewB · Dec 8, 2003

Re: 135 HP lacking power

Dont want to sound stupid here but are you running with the correct prop pitch for you boat/motor setup? That could be a possible reason for attaining low revs. Im assumming and hoping that your mechanics would have checked this but just a thought???

hawk816 · Dec 8, 2003

Re: 135 HP lacking power

Thanks for the reply....in answer to your question, yes the prop pitch is suited for the engine no problems there.

AndyL · Dec 9, 2003

Re: 135 HP lacking power

Does the motor run up to revs on no load, ie on the warm up lever?? It might be an idea to check the condition of the reed valves if you are confident enough to remove the carbs.With the plugs removed does the engine turn over by hand easily enough. Have you checked the gearbox for free movement in case a bearing was siezing up in there. The drain plug on the gearbox had a magnetic pin which will pick up metallic debris which may be another lead. AT your maximum achievable rpm is the motor running smoothly?, these motors seem to always be a bit "wobbly" at low RPM but usually smooth out as power is increased. Still svratching for a lead on this one. Andy

partslife · Dec 9, 2003

Re: 135 HP lacking power

hows it going ,you might want to check the trigger it controls the enging timing if its not advancing it could be the problem. your manual should give you a test for that.

MarineTechStudent · Dec 9, 2003

Re: 135 HP lacking power

you can check the stator with a multimeter, make sure to use a dva adapter. The wire colors are blue, blue/red, red/white, and red. You will need the manual to get the correct specs for that motor. use the red lead to the wires and black to the ground.

hawk816 · Dec 9, 2003

Re: 135 HP lacking power

Thank you to all who replied it is much appreciated. I will give all the suggestions a go and see what i find.(will post results). Oh by the way....does anyone know a simple test to check stators (secondhand)? Thank you

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