1971 Johnson 20 hp smokes at idle. Got it.

[Bearcamp]

I posted earlier about my 71 20hp Johnson smoking so much at idle and lots of oil out the exhaust. Well I found a solution to the problem. I removed the carb and accordong to the manual they want the float to set parralell to the base of the carb. All fine and dandy, I did that and no good. I've always set my floats a little lower than manufacturers specs. So I did on this. Also the mixture screw was out about 3 1/2 turns, took it in to 1 1/2, fired it up and seemed to work ok. But from idle to full throttle it was slow and sputter sometimes. Took the adjusting screw in to about 1 turn and bang. Ran great with very, very little smoke at idle , throttles up great and............idle. That baby idles like a champ. Matter of fact, I'm gonna keep this one and sell my 92 Evinrude 15hp. I like it that much. Main reason I bought this one anyways is I wanted a little more weight...............and I have one for parts. Main problem was that fuel level was too high even though it was at manufacturers specs. So think about that when you have a simalar problem.

 

[DJ]

Re: 1971 Johnson 20 hp smokes at idle. Got it.

Be careful, watch the condition of your spark plugs. Two strokes do not like lean (they'll run good) mixtures. Excess combustion chamber heat (lean) is the enemy of those engines.<br /><br />If you really want to play with mixtures, you should be using an exhaust pyrometer (temperature).<br /><br />They'll run great (lean), just before meltdown.

 

[Bearcamp]

Re: 1971 Johnson 20 hp smokes at idle. Got it.

What is an exhaust pyrometer, what do they do and where can I get one? Also, what should I look for on the plugs?

 

[DJ]

Re: 1971 Johnson 20 hp smokes at idle. Got it.

An exhaust pyrometer measures the temperature of the exhaust. A lean mixture burns hotter, to a point.<br /><br />You can accomplish similar results by monitoring head temperature with an infrared/handheld guage. Available at most tool stores.<br /><br />The head temp should not exceed 145-155 under heavy load. Even that can be tricky. Remember, you have a (raw) water cold cooling system.<br /><br />The spark plugs should be a medium tan color with no signs of hot spots (white). If you see metal transfer, onto the plugs, it's too late-damage done.<br /><br />I would realy set everything to factory spec's. The engineers that designed the engine spent mega$$$millions developing it.<br /><br />As previously stated, a lean mixture is the number one cause of two stroke engine failure.<br /><br />If the idle smoke really bothers you, decarb it and switch to a full synthetic oil. It will help.<br /><br />See decarb procedure here.<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=36;t=000016

 

[Bearcamp]

Re: 1971 Johnson 20 hp smokes at idle. Got it.

Gonna get the manual out and set everything to specs and try it again. Cause ya know, the whole problem could've been that top adjusting screw. When I started off it was turned out about 3 1/2 turns. Maybe I should've left the float level alone and checked the top adjuster first.

 

[Bearcamp]

Re: 1971 Johnson 20 hp smokes at idle. Got it.

Ok, I checked the temp and it's running around 132. Also checked the plugs after a good hard run and they looked fine. They were like a tan in color (insulator) with no deposits. The only thing I noticed was after running , I'll shut it down for maybe an hour. It starts easy on 1 pull (even 1/2 pull and til it warms a little it'll spit and sputter for about 15 seconds, then smooths right out. Think maybe it's just a little cool or should I rich it up a little? Hey thanks for all the help on this DJ and alcan. Very informative.

 

[reeldutch]

Re: 1971 Johnson 20 hp smokes at idle. Got it.

as far as i know sneezing motor means running lean to me.

 

[Bearcamp]

Re: 1971 Johnson 20 hp smokes at idle. Got it.

Yeah, I aggree. But only when it's cold for about 15 seconds. Once it get a little warm, it's fine. Maybe it's just the nature of the beast. I can live with it.