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Post by magoconnor on Sept 21, 2018 10:15:50 GMT -5
Hello.
So Im having a problem with one of my bikes a kymco super 8.
Now this bad boy has 14" rims and with the tire it amounts to a 20".
It seems like no matter what I do to it, I just cant get it past 40 mph on a flat road.
Down hill is another story...
From factory its only meant to reach speeds of about 27 mph.
Could it be, its fitted with a very low gearing, to compensate for the abnormal large tires?
As to still restain a descent acceleration but slaughter the top end from factory?
No matter how heavy rollers I run with, the bike always reaches 8000 rpms and above when I hit 39mph.
I have of cause tried different torque springs....
The jetting is good.
Setup
139qmb 72cc
stock port matched head
Leo vince exhaust
Polini variator
Naraku 18,5mm carb
Racing cam
Stock clutch
1000 rpm spring
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Post by dexameth on Sept 21, 2018 10:58:52 GMT -5
Did you pull the variator out yet and remove the boss restriction? If you've played around with the rollers then you must have... hmm.
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Post by magoconnor on Sept 21, 2018 15:36:35 GMT -5
Yes all the restrictions are removed and a shorter boss is installed.
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Post by dexameth on Sept 21, 2018 15:46:30 GMT -5
Okay, next thing I would check is belt travel with the ol' Sharpie line on the pulleys. Both variator AND clutch pulleys, this way you can see how far the belt is travelling.
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Post by magoconnor on Sept 21, 2018 20:01:16 GMT -5
Yes I have done that and I'm using the whole variator.
I think its the gears but i'm not sure, there is not a whole lot of specs on this scooter and not many people mess around with em.
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Post by KSR Moto on Sept 22, 2018 8:01:02 GMT -5
I would remove the cvt cover and turn the clutch bell by hand and see how many rotations of the bell is needed for one full rotation of the wheel
Now you have a number to compare with scoots which have smaller wheels
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Post by GrumpyUnk on Sept 22, 2018 9:33:28 GMT -5
As dumbahihi noted, count the clutch bell revolutions for one turn of the rear wheel. There is a video demonstrating that activity by 90gtvert. You can stick a bit of tape on the bell, and the same on the side of the wheel to keep track easier.
Given the diameter, the gearing should (likely) be different from the ratio of a 10" or 12" scooter. To have the same performance, it would have to be a higher number of clutch bell rotations to one wheel rotation.
tom
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Sept 23, 2018 13:24:40 GMT -5
Not sure I under stand... are you saying you are doing 8000 rpm at 40 mph and when you are on a slight downhill the RPMs and Speed both go up?
The way I understood it ( and I may be wrong) is that the bike is getting up to 8000 rpm at 40 mph. If that is the case it certainly is not geared too low. If that is the case, then my thought is that the bike just doesn’t have the hp to pull beyond 8000 rpm under load
A gear problem would be if you were turning 9500 rpms at 40
Remember, the cams in these guys are mild and are designed to give max HP at 7500 rpm. Unless you have changed it it, a 18 mm carb is what these little guys need to run best at that 7500 RPM. To get more hp, you have to turn more RPMs so a bigger cab might be your next upgrade. I know a lot of people equate carb size to displacement, but it’s really the RPM you want HP at the is limited by carb size. Everything about these little engines is designed to be 3 hp at 7500 rpms. To make it into a 8 hp at 8500 rpms, we have to change a lot of things, and carb size is one of them
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