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Aftermarket Engine/Parts
Honda Nice
Nice 110 Jetting Baseline for Keihin PE20
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<blockquote data-quote="69ST" data-source="post: 117492" data-attributes="member: 5"><p>Methinks TRG has it nailed. You cannot necessarily go by any other carburetor from another application...even OEM; there are more variable parameters than just main jet size, in play. No need to go into another longwinded tech lecture/explanation. You're pretty much limited to working with jet sizing, jet needle height settings and, possibly, float height settings, period. </p><p></p><p>Your significantly lower-than-expected peak oil temps and contradictory tuning results speak volumes...that you need to wait for higher ambient air temps. 60km/h should be about 5000rpm, if you're geared properly for the tire height. At that rpm, the engine should be breathing deeply enough to make any 22mm, or smaller, carb snap to attention. Your speed results are a little on the anemic side, too...again, assuming optimal gearing and a non-stingy speedometer.</p><p></p><p>Changing main jet sizes should impact needle height...dramatically. What you're getting, so far, makes no sense...unless something is affecting the functional air:fuel ratio in a big way. Poor atomization, as would result from an overly-chilled intake can do this. It's also the most likely cause.</p><p></p><p>I'd want to see oil temp around 100C and ambient air temp of 25C, at least. The two are related; it should be easy to get the oil beyond 100C...unless ambient temp is on the chilly side. (At 30C, an engine with this low mileage can be expected to top 110C with relatively little provocation.) Then, go back to basics. Find the rich limit at WOT. From there, you can try going one main jet size smaller, which should necessitate setting the jet needle height a few positions lower (increasing needle height). That's an educated guess, I've not worked with this, particular, Keihin carb.</p><p></p><p>As for the OEM 18mm Keihin metered air & fuel leak from the Nice...virtually non-applicable to your setup. It was calibrated on the lean side, whilst inhaling through a restrictive airbox, exhaling through a somewhat restrictive exhaust and on straight gasoline, as was widely available 10-15 years ago. Don't know what jets were used, not even the series. And jet needle height was fixed, i.e. non-adjustable.</p><p></p><p>Lastly, I'm still wondering what you're considering a "weak spot/stumble" in the midrange when transitioning to from 50% to WOT. Since this is neither a pumper nor CV type carburetor, there's always going to be a limit to the rate at which the throttle can be fully opened. Unfortunately, this is a vast gray area and tuning from behind a keyboard has its limits...</p></blockquote><p></p>
[QUOTE="69ST, post: 117492, member: 5"] Methinks TRG has it nailed. You cannot necessarily go by any other carburetor from another application...even OEM; there are more variable parameters than just main jet size, in play. No need to go into another longwinded tech lecture/explanation. You're pretty much limited to working with jet sizing, jet needle height settings and, possibly, float height settings, period. Your significantly lower-than-expected peak oil temps and contradictory tuning results speak volumes...that you need to wait for higher ambient air temps. 60km/h should be about 5000rpm, if you're geared properly for the tire height. At that rpm, the engine should be breathing deeply enough to make any 22mm, or smaller, carb snap to attention. Your speed results are a little on the anemic side, too...again, assuming optimal gearing and a non-stingy speedometer. Changing main jet sizes should impact needle height...dramatically. What you're getting, so far, makes no sense...unless something is affecting the functional air:fuel ratio in a big way. Poor atomization, as would result from an overly-chilled intake can do this. It's also the most likely cause. I'd want to see oil temp around 100C and ambient air temp of 25C, at least. The two are related; it should be easy to get the oil beyond 100C...unless ambient temp is on the chilly side. (At 30C, an engine with this low mileage can be expected to top 110C with relatively little provocation.) Then, go back to basics. Find the rich limit at WOT. From there, you can try going one main jet size smaller, which should necessitate setting the jet needle height a few positions lower (increasing needle height). That's an educated guess, I've not worked with this, particular, Keihin carb. As for the OEM 18mm Keihin metered air & fuel leak from the Nice...virtually non-applicable to your setup. It was calibrated on the lean side, whilst inhaling through a restrictive airbox, exhaling through a somewhat restrictive exhaust and on straight gasoline, as was widely available 10-15 years ago. Don't know what jets were used, not even the series. And jet needle height was fixed, i.e. non-adjustable. Lastly, I'm still wondering what you're considering a "weak spot/stumble" in the midrange when transitioning to from 50% to WOT. Since this is neither a pumper nor CV type carburetor, there's always going to be a limit to the rate at which the throttle can be fully opened. Unfortunately, this is a vast gray area and tuning from behind a keyboard has its limits... [/QUOTE]
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Nice 110 Jetting Baseline for Keihin PE20
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