Quick Idle Question

yuckfoo

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I put a new spark plug in and rode about a quarter mile at low throttle. The electrode looked white-ish, not sure if I really rode long enough. Anyway, I moved the clip from center to one below center. First thing I noticed is it started smoking when it had not done so before. The second thing I noticed was that it wanted more idle. I turned that screw again and again, probably ended up with at least two full turns towards higher idle by the time I was done.

I'm looking for general explanations/confirmation to these two questions:

Why does a richer needle setting make the engine go from no visible smoking to quite a lot of smoking? It's a sure sign that the needle is set too rich, correct?
Why was I able to turn the idle up a lot and the idle just barely got faster. I suppose that too confirms that it was too rich?

So far I can't seem to determine whether the 70 or the 72 jet is better. So, next time out I'm going to try a 75. I'm thinking it will either run a bit better or lot worse. If worse I'll at least know what too high is.
 

noah9988

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It seems like it's too rich, yes. You could turn the idle up a lot and make no difference because it's too rich. The same thing happens when you put the choke on, you can give it throttle but it won't rev up.

The spark plug and just feeling how it runs will tell you if you're rich or lean.

(Anyone feel free to correct me if I'm wrong)
 

Greg58

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If you think about what you posted you answered your own question, you raised the needle which adds more fuel which created a richer mixture, smoke. Turning in the idle screw raises the barrel but also raises the needle, that’s why it took several turn to get a good idle, as you added more air you were adding more fuel.
 

Greg58

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From my experience you have to get the jet size correct first, then adjust the needle as good as possible for 0-3/4 throttle. If one notch is too lean or rich a thin shim as cannonball suggested can help. Sometimes you have to think outside the box.
 
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