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Aftermarket Engine/Parts
Lifan
New 125 Sputters through all throttle/idle
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<blockquote data-quote="69ST" data-source="post: 180271" data-attributes="member: 5"><p>I'd order #140, 150 & 160 mains, #20 & 22.5 pilot. One of those pilot jets will be on the money. The mains are harder to guess, especially with a VM22, because the amount of vacuum (a.k.a. "pullover effect") can vary greatly, from one engine to the next. Best guess, a garden-variety L125 motor makes around 8hp. A VM22 can easily flow enough to support ~17-18hp, VM20 ~15hp. The 125cc displacement is close to the ragged edge for a VM22; you'll have no problem dialing-in the idle mixture but, the off-idle-to 1/4 throttle range is too unpredictable to make an accurate guess, without some specific experience. There are different flavors of L125/110 motors, thus it's all but guaranteed that jetting/tuning will require some trial and error. You could end up needing a #130 main, or a #170; this way, at least, you'll be close enough to limit any further guessing/testing. But...there's always that exception which proves the rule, i.e. needing a main jet that's either smaller than #130 or larger than #170. Seriously, I've installed VM22 carbs on highly-tuned (14-16hp) 125cc tunes...that ended up in the #200-220 range; there's that much variation, at WOT/peak power. I'm guessing that your L125 makes peak hp in the 6500-7500rpm range and runs out of breath in the low-to-mid 8000s; this corresponds with the expected peak hp number.</p><p></p><p>It's your machine, so the call is strictly yours alone to make. That said, I'd consider the aforementioned lifan motor, from a tuning/jetting perspective, the same as a 110. For that reason, I'd choose the VM20. Applying Boyle's law, that ~20% reduction in venturi size (cross-sectional area) will result in 20% increased airflow velocity. That will make the fuel circuits more efficient, improve atomization and deliver superior throttle response + mpg...better efficiency, all-around. That said, I'm still running a VM22 on my daily rider (110cc Honda power)...after 16 years. It starts easily, idles fairly well, but it's not perfect and never will be. I've settled for 95% "perfect" and roughly 15mpg less than the engine/bike combo should deliver. One final caveat...and this may not apply with those extra 15cc displacement...I had to re-profile the jet needle, working 0.0005" at a time, to minimize a light-throttle transient lean spot (stumble at low rpm, off-idle). I've been tuning carburetors for 50 years and I consider this kind of modification the closest thing to a black art.</p></blockquote><p></p>
[QUOTE="69ST, post: 180271, member: 5"] I'd order #140, 150 & 160 mains, #20 & 22.5 pilot. One of those pilot jets will be on the money. The mains are harder to guess, especially with a VM22, because the amount of vacuum (a.k.a. "pullover effect") can vary greatly, from one engine to the next. Best guess, a garden-variety L125 motor makes around 8hp. A VM22 can easily flow enough to support ~17-18hp, VM20 ~15hp. The 125cc displacement is close to the ragged edge for a VM22; you'll have no problem dialing-in the idle mixture but, the off-idle-to 1/4 throttle range is too unpredictable to make an accurate guess, without some specific experience. There are different flavors of L125/110 motors, thus it's all but guaranteed that jetting/tuning will require some trial and error. You could end up needing a #130 main, or a #170; this way, at least, you'll be close enough to limit any further guessing/testing. But...there's always that exception which proves the rule, i.e. needing a main jet that's either smaller than #130 or larger than #170. Seriously, I've installed VM22 carbs on highly-tuned (14-16hp) 125cc tunes...that ended up in the #200-220 range; there's that much variation, at WOT/peak power. I'm guessing that your L125 makes peak hp in the 6500-7500rpm range and runs out of breath in the low-to-mid 8000s; this corresponds with the expected peak hp number. It's your machine, so the call is strictly yours alone to make. That said, I'd consider the aforementioned lifan motor, from a tuning/jetting perspective, the same as a 110. For that reason, I'd choose the VM20. Applying Boyle's law, that ~20% reduction in venturi size (cross-sectional area) will result in 20% increased airflow velocity. That will make the fuel circuits more efficient, improve atomization and deliver superior throttle response + mpg...better efficiency, all-around. That said, I'm still running a VM22 on my daily rider (110cc Honda power)...after 16 years. It starts easily, idles fairly well, but it's not perfect and never will be. I've settled for 95% "perfect" and roughly 15mpg less than the engine/bike combo should deliver. One final caveat...and this may not apply with those extra 15cc displacement...I had to re-profile the jet needle, working 0.0005" at a time, to minimize a light-throttle transient lean spot (stumble at low rpm, off-idle). I've been tuning carburetors for 50 years and I consider this kind of modification the closest thing to a black art. [/QUOTE]
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New 125 Sputters through all throttle/idle
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