1984 Johnson 70hp will not reach high rpm

JPRidley

Recruit
Joined
Aug 1, 2009
Messages
5
My 1984 70hp 3 cylinder Johnson starts easily, will idle very smoothly, and initially accelerates well but refuses to accelerate into high rpm and will not even plane out. I have rebuilt the carbs, checked and rechecked the high speed jets, replaced the plugs, checked and replaced all the fuel lines, cleaned the fuel pump filter, made sure the gas tank is vented, made sure it is running new gas with 50:1 mixture, checked the mechanical throttle linkage for correct settings so that the carbs are opened up all the way when the throttle lever is pressed all the way, run compression checks on all three cylinders - all are within 15 lbs of each other with 130, 135, and 140, and I have checked the stator output and the rectifier/regulator output and all seem to be within specs. Ok Ladies, what could I been missing here? This is very strange and any assistance or thoughts would be most appreciated. It ran great last year.
 

22E6441

Petty Officer 1st Class
Joined
May 29, 2008
Messages
376
Re: 1984 Johnson 70hp will not reach high rpm

I'm researching a similar problem with my engine.

Your engine may be going into SLOW.

Speed Limiting Overheat Warning

Not sure about your motor, but I can apparently disconnect a tan coloured wire that goes to the top of my motor to unplug the sensor for testing purposes.
 

JPRidley

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Joined
Aug 1, 2009
Messages
5
Re: 1984 Johnson 70hp will not reach high rpm

Thanks for the suggestion. I will try this. Can you recommend a source for the Thermasticks and a sensor if necessary?:)
 

JPRidley

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Aug 1, 2009
Messages
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Re: 1984 Johnson 70hp will not reach high rpm

My wiring diagram does not show a SLOW sensor. It does show a temp switch which is connected to a horn circuit - but I do not see a connection to the power pack or the coils. Are you sure that an 84 has a SLOW circuit?
 

countvlad

Chief Petty Officer
Joined
Jun 29, 2009
Messages
439
Re: 1984 Johnson 70hp will not reach high rpm

Thanks for the suggestion. I will try this. Can you recommend a source for the Thermasticks and a sensor if necessary?:)

are yo sure you are firing on all cylinders?
 

JPRidley

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Joined
Aug 1, 2009
Messages
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Re: 1984 Johnson 70hp will not reach high rpm

Does the Stator or the Power Pack or the Coils have a "high RPM" circuit or awareness? If so I cannot find documentation of this so far. I have seen this same symptom discussed in many other threads - but so far no real solid solutions - mostly just a bunch of carb and fuel line related guesses.
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: 1984 Johnson 70hp will not reach high rpm

timing and linc n sinc. did you remove all the jets and clean them and the passages, and blow out the pick up tube in center of carb? you have 3 jets in those carbs, low, mid and high speed.
 
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