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General Minitrail Talk
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Good article on Carb Tuning
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<blockquote data-quote="69ST" data-source="post: 35477" data-attributes="member: 5"><p>It's a very good article but there are some differences between 2-stroke & 4-stroke tuning parameters. Without getting into too much detail for the moment, just be aware that air:fuel ratios need to be much leaner for 4-strokes. Stoichiometric (chemically ideal) air:fuel ratios for 4-stroke motors are - 14.7:1 at idle & part-throttle, 12.7:1 at full power WOT. 2-cycles inherently make more power for the displacement, but 4-cycle engines are much more efficient and cleaner-running. It has been my experience that motors used in CT70s won't rev-out cleanly with 12.5:1 A/F and that idle & part-throttle A/F ratios in the 13.8:1 - 14.3:1 range give the best overall balance.</p><p></p><p>Some very good & detailed explanation in the article, they just need some interpretation in places to apply to 4-cycle bike engines and other brands/models of carburetors. If you already know some of the basics, no worries. For those who are still green in the area of carburetion, when in doubt, ask questions.</p></blockquote><p></p>
[QUOTE="69ST, post: 35477, member: 5"] It's a very good article but there are some differences between 2-stroke & 4-stroke tuning parameters. Without getting into too much detail for the moment, just be aware that air:fuel ratios need to be much leaner for 4-strokes. Stoichiometric (chemically ideal) air:fuel ratios for 4-stroke motors are - 14.7:1 at idle & part-throttle, 12.7:1 at full power WOT. 2-cycles inherently make more power for the displacement, but 4-cycle engines are much more efficient and cleaner-running. It has been my experience that motors used in CT70s won't rev-out cleanly with 12.5:1 A/F and that idle & part-throttle A/F ratios in the 13.8:1 - 14.3:1 range give the best overall balance. Some very good & detailed explanation in the article, they just need some interpretation in places to apply to 4-cycle bike engines and other brands/models of carburetors. If you already know some of the basics, no worries. For those who are still green in the area of carburetion, when in doubt, ask questions. [/QUOTE]
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Good article on Carb Tuning
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