1996 70hp johnson wont run under load

JRAYks

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Jan 11, 2020
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My 96 70hp Johnson will not stay running when i put it into gear when underload. If I'm running it on the water hose ear muffs it sounds better than it has in 6 years. I'm pretty well out of my element as to how to figure out what is causing it.

I have new gas line, new gas tank , new spark plugs, new fuel filter, and new batteries.
 

racerone

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Dec 28, 2013
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23,929
You start with a compression test.----If the results are good ( even ) then test the ignition system----Good spark MUST jump a gap of 3/8" or more.----Did this problem show up suddenly ?
 

JRAYks

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Jan 11, 2020
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The motor was down for 4 years due to a broken water pump. Before the water pump went out the motor ran rough idled rough.
 

racerone

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Dec 28, 2013
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4 years to fix a water pump ?-------Did the warning horn alert you 4 years ago ?----If not then the compression test is the first step to take.----Is the motor running with VRO in service ?----If so was it tested ????-----Run with 50:1 mix if you are unsure of the automatic system !
 

JRAYks

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Jan 11, 2020
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I didnt have the extra $$ to buy the stuff to do the water pump. Buying a house and having a kid does that. There was no horn or alert it worked one season and the next it didnt work. I run the mix my grandfather has written down there theres not automatic oil system on this motor
 

awallace

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Jan 12, 2020
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10
Just off the top of my head it sounds like your high speed jet might be plugged causing fuel starvation, Or the timing may be off a bit. Try it again with the choke partially closed try adjusting it to see if you can get the engine running under load. That way you can at least identify the root cause. Its not unusual for the carb to plug up after sitting for a year let alone 4. good luck.
 
Joined
Jan 16, 2020
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Sitting that long, high speed jets, best to tear down carbs and go with a clean and new kits. High speed jets are in the bottom of the carburetor bowls so that is the first thing to gum up on those, will run like a top on a flushette all day long but will fall on it's face when under a load.
 

oldboat1

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Apr 3, 2002
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8,299
Could be the h.s. jets if it wants to throttle up, but then dies. If you can't shift into gear without stalling, I would guess it's the idle circuit. It's probably best to just disassemble the carb and soak the top and bottom (Remove the plastic carb cover.) Use a piece of soft wire to clean all openings, then blow them out with carb cleaner. Set the low speed needle valve to initial setting (probably 3 1/2 turns open +/-), and adjust from there. Warmed up and in the water, find the leanest setting that allows you to shift into gear/throttle up without stalling or lean sneezing.
 
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