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Low rpm

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MangledMike

New member
03' 50hp 2 stroke mercury emptor
Rebuilt carbs ,rebuilt fuel pump ,new fuel filters & lines,good compression all 3 cylinders.new water pump.
New cables.....will rev on its own,when in neutral.
Well over 6000 rpm.
When in the water won't spin above 3000 rpm, no matter the trim. Spark on all 3 cylinders.
After few minutes in the water it fouls plugs.
Running in barrel it doesn't foul them.
Motor is on 21' pontoon.
Any direction would be appreciated. Been a mechanic for 50years, first boat...and it's whooping me...so far.
 
Put it in the lake still on the trailer, set idle in neutral to about 850. That should give you about 650 when in forward or reverse, then in gear back out the idle mixture screw/screws 1/16 of a turn at a time and give it throttle to see if it spins faster
 
..."Also prop is still same the boat had years ago and would top out at 4300rpm. "

That's way too low for all the weight she's pushing. Add a bit of fouling on the bottom, and maybe a bit more weight on board, and you've got a problem.

I'd suggest a LOT less pitch, even if the motor over revs at WOT (which you don't want to maintain, right?)

Jeff
 
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