1972 Johnson Motor problems

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Poorbiker

Recruit
Joined
Jul 20, 2004
Messages
1
I have a 1972 ( I think) 100HP Johnson motor. It will start right up with the chock and runs excellent until you start going about 3/4 throttle, then the motor will start missing and hesitating. I slow the boat down and shut the motor off. Motor is warmed up and to get it started again I need to chock it again. After it starts and it runs fine until 3/4 throttle. Put new plugs in it and supposedly carbs tuned. Any ideas what might cause this. I have also checked to see if the bulb is hard when starting to hesitating and it seems hard but not rock hard.
 
P

papasage

Senior Chief Petty Officer
Joined
Jan 12, 2003
Messages
785
Re: 1972 Johnson Motor problems

carbs tuned ? carbs need to be rebuilt soaked in carb cleaner a blown out with compressed air.
 
C

craigvalk

Seaman
Joined
Jul 23, 2003
Messages
73
Re: 1972 Johnson Motor problems

I agree on the carbs. Likely they are gummed. "Carb tuning" could mean just playing with the low speed mixture screws. More than likely a good rebuild and cleaning is in order. I'd do that first and then go from there.
 
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skeezx01

Petty Officer 2nd Class
Joined
Jul 14, 2004
Messages
105
Re: 1972 Johnson Motor problems

yup, carbs. junk in the power circiut. DON"T soak in regular carb cleaner. i have been told by a greybeard boat mechanic thad doing so will eat up the porous cast metal in the fuel bowl, said only to use areosol. havn't personally tried to soak em cuz i don't have any carbs to waste
 
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