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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: 117907" data-attributes="member: 5"><p>I'm glad that you didn't misread my previous post. I'm trying to be brutally honest and not offend. Machinery has no social grace whatsoever...and that's what we're dealing with. It either works properly, or it doesn't.</p><p> </p><p>Factory rating for your motor is 9.5hp@8000rpm. Seems a trifle optimistic, imho, but based on what I've observed (i.e. real world speed runs), it's at least plausible. A fully broken-in & optimally setup 110 Nice should pull 100km/h under "normal" (i.e. on the flat, minimal headwind) conditions. A little less when riding into a strong headwind a bit more with a tailwind. With the carb & exhaust you're running, there might be another .5-1.0hp, as compared to the OEM-stock, as-installed, setup. Even that's no bfd...another 4-5km/h, tops, and only under ideal conditions, at that. OTOH, even if you're down 1hp, the top end speed reduction would be small. Seat-of-the-pants dyno results would be virtually the same, up to about 90km/h, as torque would be unaffected.</p><p></p><p>FWIW, I do use a wideband O2 meter, when in doubt. I understand your reluctance to test a #140 main, I feel the same way. Smallest main I've ever tested successfully with this engine/carb combo has been #145. That said, pump gas formulations have changed significantly in recent years. I've no idea if Mikuni changed anything inside these carbs. Fact is, there's no practical way to verify either. Even when I began the Nice motor odyssey, over a decade ago, there was always a +/- one main jet size range, from one to the next. I just chalked it up to manufacturing tolerances. A minuscule change inside a carburetor can have a huge impact. If you've been following anotherct's thread, his engine ran best with a #150 main...that was verified with an O2 meter, in realtime. Same motor, carb, intake & exhaust...and about the same observed top speed (ran it up to 62mph - 104km/h), briefly since the rebuild was fresh.</p><p></p><p>Though (ostensibly) unlikely, it's possible that Honda changed the cam profile. Semi-automatics & manuals had different PNs. I'd assume the semi-auto grind would be more conservative, for added low-end torque. </p><p></p><p>So, consider the potential variables in this equation: fuel, carb & cam changes. A 140 jet is only one size smaller than what has, hitherto, been the lean limit. Below #150, the size increments are -5, instead of -10. If Mikuni is consistent within their own jet size nomenclature, you're only a half-size below the previously accepted threshold. </p><p></p><p>I'd have tried a VM20 but, that's a little too "I told you so", for now at least and probably unnecessary. Discard the old <school> preconceptions. Go back and verify that your intake outlet is perfectly aligned with the intake port and that the carb end is aligned with the insulator & carb throat...which is really easy to do, just remove the slide and look. Verify that the rubber O-ring that seals the main jet well to the bowl is healthy & intact. If it's nicked, torn or crunchy, replace it. A leak there can richen the mixture beyond control. Next up, source a 140 & 145 main, set the jet needle at max height (C-clip on the lowest groove) and see what it does. If it still goes into rich misfire, raise the C-cilp 2 grooves at a time & restest as needed. Start with fresh gasoline and a new plug. As I've mentioned previously, this carb can be a temperamental sumbitch to get right. At most, you can be on cusp with two main jet sizes and two jet needle settings per jet. When you go just below the rich threshold, you'll know...the motor will rev-out, with enthusiasm, right up to redline.</p><p></p><p>Here's a kicker...when you have the choice between two different main jets that will allow full WOT rev-out, the jet needle height can have a larger effect on part-throttle mixture than the jet size & needle height will on WOT air:fuel ratio. Typically, the smaller jet, with the jet needle 3-4 steps higher, will produce part throttle A:F ratios about .5 to one full point richer and about .3-.4 leaner at WOT. I like to see about 12.5-12.6:1 at WOT, running pump gas. That said, 12.8-12.9:1 is still plenty safe. When in doubt, check the plug. Even with shitty 2014 pump gas, it's easy enough to see a black or lily-white plug tip. Burnt VHT on the headpipe is pretty hard to miss, also.</p><p></p><p>Bottom line, if the VM22 cannot be tamed, it'd be the first & only one...no exaggeration.</p></blockquote><p></p>
[QUOTE="69ST, post: 117907, member: 5"] I'm glad that you didn't misread my previous post. I'm trying to be brutally honest and not offend. Machinery has no social grace whatsoever...and that's what we're dealing with. It either works properly, or it doesn't. Factory rating for your motor is 9.5hp@8000rpm. Seems a trifle optimistic, imho, but based on what I've observed (i.e. real world speed runs), it's at least plausible. A fully broken-in & optimally setup 110 Nice should pull 100km/h under "normal" (i.e. on the flat, minimal headwind) conditions. A little less when riding into a strong headwind a bit more with a tailwind. With the carb & exhaust you're running, there might be another .5-1.0hp, as compared to the OEM-stock, as-installed, setup. Even that's no bfd...another 4-5km/h, tops, and only under ideal conditions, at that. OTOH, even if you're down 1hp, the top end speed reduction would be small. Seat-of-the-pants dyno results would be virtually the same, up to about 90km/h, as torque would be unaffected. FWIW, I do use a wideband O2 meter, when in doubt. I understand your reluctance to test a #140 main, I feel the same way. Smallest main I've ever tested successfully with this engine/carb combo has been #145. That said, pump gas formulations have changed significantly in recent years. I've no idea if Mikuni changed anything inside these carbs. Fact is, there's no practical way to verify either. Even when I began the Nice motor odyssey, over a decade ago, there was always a +/- one main jet size range, from one to the next. I just chalked it up to manufacturing tolerances. A minuscule change inside a carburetor can have a huge impact. If you've been following anotherct's thread, his engine ran best with a #150 main...that was verified with an O2 meter, in realtime. Same motor, carb, intake & exhaust...and about the same observed top speed (ran it up to 62mph - 104km/h), briefly since the rebuild was fresh. Though (ostensibly) unlikely, it's possible that Honda changed the cam profile. Semi-automatics & manuals had different PNs. I'd assume the semi-auto grind would be more conservative, for added low-end torque. So, consider the potential variables in this equation: fuel, carb & cam changes. A 140 jet is only one size smaller than what has, hitherto, been the lean limit. Below #150, the size increments are -5, instead of -10. If Mikuni is consistent within their own jet size nomenclature, you're only a half-size below the previously accepted threshold. I'd have tried a VM20 but, that's a little too "I told you so", for now at least and probably unnecessary. Discard the old <school> preconceptions. Go back and verify that your intake outlet is perfectly aligned with the intake port and that the carb end is aligned with the insulator & carb throat...which is really easy to do, just remove the slide and look. Verify that the rubber O-ring that seals the main jet well to the bowl is healthy & intact. If it's nicked, torn or crunchy, replace it. A leak there can richen the mixture beyond control. Next up, source a 140 & 145 main, set the jet needle at max height (C-clip on the lowest groove) and see what it does. If it still goes into rich misfire, raise the C-cilp 2 grooves at a time & restest as needed. Start with fresh gasoline and a new plug. As I've mentioned previously, this carb can be a temperamental sumbitch to get right. At most, you can be on cusp with two main jet sizes and two jet needle settings per jet. When you go just below the rich threshold, you'll know...the motor will rev-out, with enthusiasm, right up to redline. Here's a kicker...when you have the choice between two different main jets that will allow full WOT rev-out, the jet needle height can have a larger effect on part-throttle mixture than the jet size & needle height will on WOT air:fuel ratio. Typically, the smaller jet, with the jet needle 3-4 steps higher, will produce part throttle A:F ratios about .5 to one full point richer and about .3-.4 leaner at WOT. I like to see about 12.5-12.6:1 at WOT, running pump gas. That said, 12.8-12.9:1 is still plenty safe. When in doubt, check the plug. Even with shitty 2014 pump gas, it's easy enough to see a black or lily-white plug tip. Burnt VHT on the headpipe is pretty hard to miss, also. Bottom line, if the VM22 cannot be tamed, it'd be the first & only one...no exaggeration. [/QUOTE]
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Nice 110 Jetting Baseline for Keihin PE20
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