First I topped off
the carburetor with oil
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Then I pulled the spark plug.
That's fouled!
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I put the colortune in,
and got a very yellow spark. Way too rich, and hence the fouling.
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Here's a video of the colortune
in action, showing the regular yellow spark. I was actually surprised at how slow it was blinking, but I guess 600 rpm for 4 cylinders is only about twice a second spark. [Video, 1.9M]
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I adjusted the richness
on the bottom. There's a spring maintaining the adjustment, which seems a bit slippy, and probably explains how it easily gets out of tune.
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And presto, the spark turns blue.
I tuned it to where the spark just starts to turn blue.
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Tuning method #2
(suggested by Haynes Manual) is the lift method: using a wire, lift the carb cylinder up a small amount, and it should just slightly increase RPMs if it's in tune. When I tuned it to the colortune, it would actually decrease RPMs under the lift test. I trust the colortune, and I don't have a problem with acceleration, so it seems to work.
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Then try to match vacuum
between the carbs. This proved difficult. I have a vacuum gauge, but it would generally go off the chart even at low RPM, so it was impossible to match. I tried doing it by sound instead, but I couldn't distinguish much difference between the hiss.
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