1972 Johnson Motor problems

[Poorbiker]

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.

 

[papasage]

Re: 1972 Johnson Motor problems

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

 

[craigvalk]

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.

 

[skeezx01]

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