Mercury 50hp 4 stroke no power/low RPM

SteveMu

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Jun 18, 2013
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4
I have a new to me 2000 50hp 4 stroke bigfoot. The carbs were dirty so I cleaned them in a sonicator and replaced the nozzles. All the jets were clear but carbs 1,2,&3 had the wrong nozzles and the nozzle in #4 was in two pieces. Motor has good compression, starts fine and has a smooth idle but it lacks power (stays around 3000 rpm). I have checked the stator, fuel pump, coils, thermostat, and tried new plugs but no difference. Squeezing the ball while running has no effect. I don't know for sure but I suspect the previous owner had this issue as well. I am at a loss as to what to try next, any ideas????
 

SteveMu

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Jun 18, 2013
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4
Re: Mercury 50hp 4 stroke no power/low RPM

I changed the fuel line since I had the old type with the red lettering. I cut it open and sure enough it was seperated. Took the boat out but no change. I did notice that the new fuel line was leaking and sucking air at the tank. The motor got hot and the alarm came on. Pulled the plugs and 1 and 3 are clean, 2 is black and 4 is slightly black. I also noticed that some of the exhaust is coming out around the anodes. Is this normal?
 

quicktach

Petty Officer 1st Class
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Aug 24, 2012
Messages
394
Re: Mercury 50hp 4 stroke no power/low RPM

Sounds like possibly an electrical problem. Getting good spark ? I'd get the CDI manual and follow the book ---troubleshooting the entire electrical system. Possibly an advancing issue ? There could be all kinds of things wrong, so do one system at a time.
Overheating ... lean carb ? Oil/gas mix ending up too lean...
Are you getting water out the pee tube ??
 

SteveMu

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Jun 18, 2013
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Re: Mercury 50hp 4 stroke no power/low RPM

Did DVA test and got a steady 220V from the stator running just above idle. The manual says to measure reverse polarity at the coils and it should be 160V-280V but I only get about 1V. When I change polarity I get 150V which seems low. Spark has no trouble jumping a 7/16" gap but it seems more orange than blue. I'm leaning towards a bad CDI.

I think the overheating issue was caused due to the fuel tank connector. Pee stream is strong.
 

SteveMu

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Jun 18, 2013
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Re: Mercury 50hp 4 stroke no power/low RPM

I am pretty sure I solved the low power issues. Dug into the carbs again and the o-ring on the plug that holds the nozzle was dried out and cracked on all 4 carbs letting gas bypass the jets thus flooding the motor. The boat has no trouble getting up on plane now but the overheating issue still exists. The water pump is new and I pulled the lower leg and everything is clean. I did notice that the pee stream is not as strong as it was. Is there a way I can check the grommet without pulling the power head? I figured I had sucked up some sand in shallow water while testing on the trailer but everything looks clean. Previously the pee stream was very strong.
 
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