Jetting a non-standard carburetor for an engine, especially when no one has tried the combination before, is an extremely time-consuming process of trial and error. I reasoned that the original jetting would be a close match, or at least a decent starting point, because the three carbs had previously been mounted to a Triumph Trident, with each feeding a 250cc cylinder. What I didn't take into account though, was the possibility that the previous owner may have jetted it TOTALLY WRONG.
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| This is becoming an annoyingly familiar sight... |
Mikuni carbs have three main fuel circuits: the pilot circuit for 0 to 1/4 throttle, the midrange circuit for 1/4 to 3/4 throttle, and the main circuit for 3/4 to full. After weeks of fiddling, testing, and tinkering, I have determined that the pilot circuit was JUST ABOUT right, the midrange was extremely lean, and the main was extremely rich. In fact, the disparity between midrange and main was so large, that it created the illusion that it was jetted correctly, but had an air leak/low range stumble. The rich main supplemented the lean midrange and they compensated for each other, while causing poor power and a tendency to stall at low throttle.
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| Needle Jet Swap |
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| Seriously, I've had enough of propping the tank up... |
I think I'm pretty close to getting it dialed in mostly right, and will post the final settings when I have them. Though, I think I should bring it in to a tuning shop and have them doublecheck it...and also rebuild the brakes....possibly replace the clutch plates...sooner or later it will be "done"!
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