1987 Johnson 20 coughing bad

[mafhuntfish]

Hi All - I have a 1987 Johnson 20 that idles smooth but coughs really bad when you throttle it up. I've cleaned the carb twice now, checked the reed valves - what I could see through the intake they looked fine, and replaced the top coil. The top plug was/is real wet and the bottom plug is dry & black. I just did a compression check & it was decent @ 99 & 96. Any Ideas about the coughing?

 

[jasper60103]

Re: 1987 Johnson 20 coughing bad

Did you test the spark? Top coil is still suspect. Also, if the coil is not grounded, it still won't fire. That one bit me once.

 

[mafhuntfish]

Re: 1987 Johnson 20 coughing bad

Just checked spark with an inline tester - spark bright & clear on both cylinders - could a bad power pack cause intermittent spark on only the top cylinder?

 

[jasper60103]

Re: 1987 Johnson 20 coughing bad

Just checked spark with an inline tester - spark bright & clear on both cylinders - could a bad power pack cause intermittent spark on only the top cylinder?

I'm thinking it could be carb related. Do you remember if you replaced the nozzle gasket? See (#7) on diagram. Very easy for that part to fall out or be missed during carb assembly. That could cause high speed flow problems. Maybe BK will chime in.

 

[mafhuntfish]

Re: 1987 Johnson 20 coughing bad

nozzle gasket was definitely installed

 

[jasper60103]

Re: 1987 Johnson 20 coughing bad

nozzle gasket was definitely installed

Hmmm. Well, I hate to guess and be wrong on the power pack. I've done that before and it didn't solve my problem. Hopefully others will chime in soon.

 

[mafhuntfish]

Re: 1987 Johnson 20 coughing bad

Thanks & I'm really not looking forward to spending $100 if that's not the problem .. I appreciate all your help

 

[G DANE]

Re: 1987 Johnson 20 coughing bad

HOW are you throttling it up - if it is by the carb linckage alone, it will cough or shoot since the ignition isnt advanced before throttle butterfly is opened. If you do it right, by the external throttle linckage, and it still coughs, something else is wrong. Have you noticed when you advance throttle, the little cam on the stator plate has two marks. Thr roller on the trottle linckage shoul be at least right between those two marks before throttle butterfly starts to open. Be very carefull checkint this. Adjusting can be made on the socket at throttle shaft or by adjusting length of vertical throttle linckage -depending of year/model. You could aslo have an airleak, making the lean cylinder suck in false air. A hose that has fallen of, leaking gasket for fuel pump - or so.

 

[mafhuntfish]

Re: 1987 Johnson 20 coughing bad

great news - adjusted linkage so that the throttle roller stays on the cam until just past the marks & the motor runs smooth at all throttle settings - Thanks to all who helped ....

 

[jasper60103]

Re: 1987 Johnson 20 coughing bad

Great, glad to hear it was a simple fix.