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1965 9.5 HP Johnson MQ-11C - WOT Problem

E

ebowles

Member
Hello Gentlemen....I have posted before about my old "turtle" motor and have received much help from this forum....thanks to all! She's had a litany of issues to conquer, and I have tackled each one as they've arisen. After finally convincing myself that she was "perfect" in the tank, I made time yesterday to take her to the river with my trusty 15 ft. aluminum jon boat.

She started right up as expected and, after a warm up period, I let her rip. She shot out of the hole like a demon....no miss, hesitation, all good. However, after reaching top rpm, she acted as though she couldn't completely unwind. Don't know how to describe it actually, but something is keeping her from completely realizing WOT. I spent the next hour stopping, starting, retrying.....final result was always the same. She pushes my boat at around 10 mph with only me in it, so she's making a lot of rpms....just not topping out.

Any thoughts? I should mention, all carb, ignition, fuel parts are brand new.

Thanks!
 
Front motor mount ?----Throttle plate going wide open ?-----Choke plate staying open ?----Post compression numbers again.
 
Racer.....hope you're doing well.....the front motor mount was replaced this spring when I tore thru the whole thing....the throttle plate is definitely going wide open and the choke plate remains open as it should....compression numbers just taken are in the mid 70's each cylinder. One thing I noted when I removed the spark plugs to insert the compression gauge; the top plug was very dry while the bottom plug had lots of black and some wetness....both of these plugs were clean before I did the load test yesterday........hope that helps some.
 
Does spark jump a gap of 5/16" or so on a test device , yes or no ?----Have you inspected / replaced diaphragm on the fuel pump ?
 
Diaphragm on fuel pump is new. But damn, when I went to do another spark test (which I've done countless times on this motor), I'm only getting an intermittent spark on the top cylinder......it's there most of the time, just every once in a while doesn't show up. I'm tired of screwing with these "Amazon points" so I'm going with OEM this time and will rebuild the entire magneto system. Thanks Racer..
 
Check plug wires where they come out of the magneto plate.----There is a 90 degree bend that has been known to have cracks.----- Spark arcs to ground there.
 
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