1985 johnson 20hp wont run full throttle

[jstme]

ok so I have cleaned the carb, decarbed with seafoam, changed the plugs. It was running fine 2 weeks ago would throttle up good, idle good, and everything. yesterday I start it, it was running a little rough at idle and at full throttle it would never get the rpms up.....mabey about the same as 1/4 throttle. back at the dock I pull the lid off and manually moving the throttle it will rev up fine. left lid off and went back out...opened it up but it will not get up to rpm under load like it does in neutral. Any ideas?

 

[Daviet]

Re: 1985 johnson 20hp wont run full throttle

Is it firing on both cylinders? Spark and compression good on both cylinders?

 

[larryg]

Re: 1985 johnson 20hp wont run full throttle

if you get it squared away let me know.having basically the same problem.ran great then it wont open up,runs like a 10hp.

 

[jstme]

Re: 1985 johnson 20hp wont run full throttle

spark and comp good on both cyl.

 

[Daviet]

Re: 1985 johnson 20hp wont run full throttle

All it takes is timed spark, compression and fuel to make your engine run. Will your spark jump a 7/16" air gap? What is your compression? Plugs in good shape?

 

[jstme]

Re: 1985 johnson 20hp wont run full throttle

it runs fine except under load, then it wont throttle up past 1/4 throttle. I will take comp readings again tomorrow if I get time....but if I remember correctly they were both right around 120

 

[larryg]

Re: 1985 johnson 20hp wont run full throttle

while idling take top plug wire off then bottom.what happens?if the engine bogs on both its ok,if not then the cylinder isnt working,could be coil,powerpak,wire,or a reed is broke.let us know

 

[watergecko]

Re: 1985 johnson 20hp wont run full throttle

Link n sync?

 

[Monte1961]

Re: 1985 johnson 20hp wont run full throttle

With cowling off and running in gear, at wot, is the carb/s opening all the way? Next when you say bogs, Does it smell like it's running rich or not getting enough fuel? Post back and let us know!

 

[jstme]

Re: 1985 johnson 20hp wont run full throttle

it doesnt really bog, just never gets up to speed or rpm like it will in neutral. Yes carb is all the way open, I thought of that and even reached in and manually made sure it was opening up all the way. im still stumped, mabey this evening I can get exact compression readings.

 

[ICEMAN-73]

Re: 1985 johnson 20hp wont run full throttle

I had the same motor a few years back and had the same problem! it ended up being all in the remote and linkage. finaly got it all working as it should than I sold the boat.