Old Johnson 3.0HP

[warrenmarkus1]

I have recently got a old Johnson 3.0hp twin cylinder outboard which was a non runner.
I have got it to start, and run, but am having problems getting it to idle, and rev properly.
The plugs are new and set to 0.5mm, as are the points.
Fuel mix is 20:1 as written on the tank. There is a spark on both cylinders, and both plugs are firing. The engine seems to run better with the intake silencer not fitted. The plugs are blackish-too much fuel?

Does anyone know the settings for carb mixture screws, or the resistance values (or other method) to check the magneto coils?
Thanks

One coil has a green coloured plastic housing, while the other is brown, and I am not too sure if this has a bearing

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[supermalc]

2 strokes require crankcase compression to transfer the fuel/air mixture to the cylinder. This requires good crankshaft seals, something often lacking in worn engines.



<hr width=100% size=1>Malcolm.
<A target="_blank" HREF=http://geocities.com/malcsworld/>http://geocities.com/malcsworld/</A>
Take a look at my boating pages.

 

[andy01842]

I don`t know this engine but if the crankshaft seals are worn the engine would run weak, if the plugs are black it is runing rich. I would clean the carb out and check the Float a float needle if it got one. A good starting point for the mixture screw is 1 to 1 ½ turns out from fully in.

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[William_H]

The spark plug leads should measure less than a few thousand ohms to ground. That will be the conduction of the leads and the coils. Any thing higher would probably be suspect leads.
The Johnson 6 I have has mixture adjustable from the outside and is set for best speed at low throttle settings. This setting does not much effest the operation at high power settings. Yes there are reed valves in the crankcase under the carby that could cause trouble but don't usually. Probably it is running too rich with black plugs which I think requires tightening of the mixture screw. it may be the other way round to lean the mixture. Set it once it is warm for smoothest fastest idle. Try also cleaning the carb and make sure the timing change mechanism works to advance the timing by moving the under flywheel base plate when the throttle is advanced. It should be a good little motor if the 6 is anything to go by. regards will

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[floatything]

This link http://www.bosunsmate.co.uk/johnson_4_part 1.htm should have sent you to a site giving you everything you need to know about getting Johnsons running but somehow the shortcut won't work when I wrote it as a clickable link - SO try going to this one... <A target="_blank" HREF=http://www.bosunsmate.co.uk/>http://www.bosunsmate.co.uk/</A> and then selecting "articles" and you will see a link to the Johnson pages (4 of them) at the bottom.

HTH

Floatything

<P ID="edit"><FONT SIZE=-1>Edited by floatything on 29/08/2004 11:15 (server time).</FONT></P>

 

[ex-Gladys]

...the Evinrude 3 from the same era (same OMC engine) runs 50:1....

<hr width=100% size=1>Larry Botheras

Anderson 26 "Amber"

 

[floatything]

My Johnson 4 horse twin is marked 100:1 on the tank - but I run it at 50:1 and it seems happier. 20:1 seems a bit on the rich side to me. Even my old seagull only has 25:1

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[warrenmarkus1]

It is a very good point about the mixture, I actually worked out the 20:1 ratio from the text on the engine. But I will try this, and cleaning out the carb (again!) over the weekend.
Thank you all for your advice!

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