1990 20HP Johnson "cuts out" after extended idle

[tacoma_2002]

I have a CRESB Johnson 20HP that runs like a champ...however...the last of the season it started acting like it wanted to "cut out" after extended idle. Even with new plugs it shows the same symptom.

Fuel is non ethanol 87 octane mixed 50:1 with Pennzoil oil.

When idling for atleast 5 minutes or more and start to open the engine back up to throttle (gradually or all at once) it sounds like you turn the engine completely off then back on...off then back on...

You can rip the throttle a few times in neutral and same result...you can keep working the throttle and eventually it'll catch back up. I've also tried spraying a bit of fuel into the carb with the primer and it just floods the engine. It'll run WOT to 1/4 throttle all day long...but any extended idle time (5 minutes or more give/take) it acts this way...and doesn't always do it...the problem is more consistant after the engine is hot.

I know this very broad range of things that could be happening...just needing to know where to start looking...

 

[Bosunsmate]

Re: 1990 20HP Johnson "cuts out" after extended idle

Motors run hot at idle, might be a failing coil.
DO a spark check with a spark tester when its idled for that time

 

[Daviet]

Re: 1990 20HP Johnson "cuts out" after extended idle

If the spark checks out OK, you might check the low speed needle valve adjustment.

 

[ronward]

Re: 1990 20HP Johnson "cuts out" after extended idle

I had an older model that did the same thing. Re-adjust your low speed needle...get it dialed in an it will run like a top