johnson 150 problems at 3800 rpm

firejunky

Seaman Apprentice
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Sep 30, 2009
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38
I have a 1986 Johnson 150. It runs perfect up to 3800 rpms. as soon as it gets to 3800 it starts cutting out, like a dead miss. I can throttle back a little and it runs fine. I recently replaced a power pack on one side to cure another problem i was having. Could this be a problem with the stator?
This is a new boat to me I have only had it in the water 5 times.
 

tashasdaddy

Honorary Moderator Emeritus
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Nov 11, 2005
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51,019
Re: johnson 150 problems at 3800 rpm

could be clogged high speed jet in one of the carbs. could be coil heating up and failing, could power pack heating up and failing. suggest using an induction timing light, to make sure you are firing on all cylinders. have you checked your compression.
 

firejunky

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Re: johnson 150 problems at 3800 rpm

Yes the compression on all cyl. are in the high 90s.
 

emdsapmgr

Supreme Mariner
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Dec 9, 2005
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11,551
Re: johnson 150 problems at 3800 rpm

Tas has given you some excellent advice. Take a friend and an inductive timing light with you next time out. Run it up to 3800 and check all 6 plug wires with that inductive timing light. If you have solid, ryhthmic flashes on all 6 plugwires-then look to fuel as a likely cause. Add the fuel pump to your list of items to check. Compression is ok for that model.
 

James R

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Feb 1, 2007
Messages
2,660
Re: johnson 150 problems at 3800 rpm

Cleaning of carb's is so often ignored resulting in engine failure due to lack of lubrication. If you have no history on this motor the safest way to go will be to strip and clean the carbs and replace the water pump impeller and lower unit oil.
The information relating to ignition is excellent. TD is an expert in these motors.
 

firejunky

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Sep 30, 2009
Messages
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Re: johnson 150 problems at 3800 rpm

Thanks for the info. I just started replacing the carpet, So hopefully it will warm up soon and i can get out on the lake and figure out whats going on.
 

James R

Commander
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2,660
Re: johnson 150 problems at 3800 rpm

Something I forgot to mention.
Recently I rebuilt a 1993 150 and during break in I experienced a similar problem. I was running on a six gallon tank with the standard fittings. Not enough fuel above 3K. Switched to the main inboard tank and the problem disappeared. No problem since.
The horn was sounding similar to an overheat.
I still stand by my first thought re the carb cleaning. This is a must if you don't want engine failure due to lack of lub.
 

firejunky

Seaman Apprentice
Joined
Sep 30, 2009
Messages
38
Re: johnson 150 problems at 3800 rpm

Thanks for all the advice. It really seems like a timing problem to me. My Wife and I just had a new baby girl two weeks ago, and I just don't have the time right now to mess with it. I think I will take it to the shop and let them check it out.
 

firejunky

Seaman Apprentice
Joined
Sep 30, 2009
Messages
38
Re: johnson 150 problems at 3800 rpm

Well my Boat mechanic has turned out to be a parts changer. One power pack and a timer base later and the motor still won't run at high RPMs. I think i can change parts cheaper than paying him to do it.
I think I'm going to start with cleaning the carbs. Can someone tell me which carb kit to buy?
I also found one of the coils that has leaked some shiny black liguid at some point. The liquid hardened on the engine. The coil is on the same side of the engine as the new power pack.
 
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