83 50hp Johnson revs up and down constantly! Please Help

A

akslednecks

Cadet
Joined
May 19, 2011
Messages
7
Motor starts fine but it revs up and down constantly no matter what the throttle position is. When im on the water i can get it to run fine for a few minutes at open speeds. Then all of a sudden it falls on its face and starts reving up and down. New plugs and gas with seafoam. Cleaned carbs still acting the same. Then every once in a while in the driveway it will idle fine, but when i give it throttle it starts reving up and down. Its a constant up and down and will run for ever. Motor starts easily. 125psi compression in both cyl. I dont know what to do. It almost sounds electrical. Any help would greatly be appreciated. Thank You
 
D

Daviet

Fleet Admiral
Joined
Sep 24, 2008
Messages
8,958
Re: 83 50hp Johnson revs up and down constantly! Please Help

When you cleaned the carbs did you remove the high speed jets and clean them?
 
Joe Reeves

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
Re: 83 50hp Johnson revs up and down constantly! Please Help

This may not be your problem, BUT..... Having the throttle linkage between the carburetors adjusted wrong such as when at an idle, One throttle butterfly closed and One butterfly slightly open will cause the problem you speak of. They must both open completely (horizontal) and close completely at the same time.
 
A

akslednecks

Cadet
Joined
May 19, 2011
Messages
7
Re: 83 50hp Johnson revs up and down constantly! Please Help

where are the high speed jets located? would they affect idle also
 
A

akslednecks

Cadet
Joined
May 19, 2011
Messages
7
Re: 83 50hp Johnson revs up and down constantly! Please Help

I checked the butterflies only visually, i did not get technical on them, just took apart and cleaned them, everything looked pretty clean. Is there some literature i can find on the web that would show me how to tear down and rebuild the carbs.
 
A

akslednecks

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Joined
May 19, 2011
Messages
7
Re: 83 50hp Johnson revs up and down constantly! Please Help

i dont see any adjustment for the carbs ie: air/fuel ratio.
 
A

akslednecks

Cadet
Joined
May 19, 2011
Messages
7
Re: 83 50hp Johnson revs up and down constantly! Please Help

ok thank you very much. i read the top secret file and im gonna start over. thank you for your help, i will post back later.
 
D

Daviet

Fleet Admiral
Joined
Sep 24, 2008
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8,958
Re: 83 50hp Johnson revs up and down constantly! Please Help

Let us know how it turns out for you.
 
A

akslednecks

Cadet
Joined
May 19, 2011
Messages
7
Re: 83 50hp Johnson revs up and down constantly! Please Help

ok rebuilt carbs agian, they were spotless. removed flywheel and cleaned contacts on stator. motor started and ran a little better. but still revs up and down. put a test light on plug wire and found top cyl. has intermittant spark. wondering how to test the coil, rectifier and power pack. going to replace plug wires. it did shock the snot outa me so it might be the wire.
 
A

akslednecks

Cadet
Joined
May 19, 2011
Messages
7
Re: 83 50hp Johnson revs up and down constantly! Please Help

Found the problem! Traced the wires to look for bad spots and found the red wire on the rectifier to broken or hanging on by a thread. I guess it was close enough that it would arc and fire then the motor would jerk and pull the wires away. Went and picked up a free boat this afternoon that has a newer model 50hp johnson with electric trim. Motor supposidly is blew up but it looks real good and turns over. Took the rectifier off of it and put it on my boat and sounds awesome. Crisp throttle response. Thank you guys for all the help. I will try to help someone as i will need help again im sure. Thank for caring for the new guys!
 
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