Post by ccr on Nov 14, 2014 3:05:49 GMT -5
a smaller carb will provide a faster start with a good low speed throttle response due to its higher flow velocity.
a bigger carb will provide a slower start with a good mid range and high speed throttle response and allow you to reach higher horsepower levels on a BBK or even some stock setups.
however, going too big will destroy your off the line acceleration to the point where you would never reach your top speed. the flow velocity would not be able to pull enough fuel from the jet no matter how big it is, and the fuel that does mix with the air will not atomize with the air causing an uneven and unstable burn.
choosing the carb will depend on 3 main factors.
1, how fast you want to go / how fast you want to reach that speed.
2, how high your rpm settings are and what your gear settings are.
and finally 3, what the ambient temperature of the intake air is. (in a hot country there is less air density and a bigger carb is needed to compensate for the lack of cold dense air)
so if your driving in the city and you only get 2 blocks before you have to stop at the next set of lights, you should get a smaller carb, because your scooter needs to get up and go quickly. theres no point having a scooter that can go 200km/h but takes 5 minutes to reach that speed. however if you are driving longer distances and you have a lot of time between stops you can use a bigger carb to achievea higher top speed. how long are you prepared to wait for it?
another thing is engine rpm. if you install a bbk and use an original crank, that makes it more of a high rpm build. because the bore is bigger than the stroke the piston does not have to travel so far between revolutions. this means a higher rpm can be achieved and it can accelerate through that rpm faster. if you lighten the variator weights and use a bigger carb, this will allow you to rev higher and the time required for the engine to get up to its ideal flow velocity will be reduced.
for example
my stock 100cc yamaha engine came with a cvk24
it was pretty slow to reach a top speed and not very fast off the line. topped out around 95km/h
so i changed to a cvk30, big mistake on my part. i got an even slower start and only a little gain in top speed. 105km/h
then i upgraded the engine to 128cc. and it was faster off the line and had a much better top speed. something like 108km/h.
after that my friend (ex racing champion and racing bike builder) suggested i use a smaller carb and i was reluctant to at first. but after trying it on and a quick rip around the block..
it was like the beast had been set free finally and all the other mods i had made seemed to have finally paid off.
i took it out of the city and hit it hard!
KEHIN CVK26
it went off the clocks at 120km/h and kept going
i can only guess it topped out at 125km/h
so the moral of the story is, start small and work your way up. test as many sizes as you can before you buy one. i'm sure if you know someone with a keen interest in bikes they will have a few laying around that you can try out. if not then maybe a local junk yard can help you out
Read more: itistheride.boards.net/thread/7015/high-upjet-when-doing-bbk?page=1#ixzz3J1ngiaSq
a bigger carb will provide a slower start with a good mid range and high speed throttle response and allow you to reach higher horsepower levels on a BBK or even some stock setups.
however, going too big will destroy your off the line acceleration to the point where you would never reach your top speed. the flow velocity would not be able to pull enough fuel from the jet no matter how big it is, and the fuel that does mix with the air will not atomize with the air causing an uneven and unstable burn.
choosing the carb will depend on 3 main factors.
1, how fast you want to go / how fast you want to reach that speed.
2, how high your rpm settings are and what your gear settings are.
and finally 3, what the ambient temperature of the intake air is. (in a hot country there is less air density and a bigger carb is needed to compensate for the lack of cold dense air)
so if your driving in the city and you only get 2 blocks before you have to stop at the next set of lights, you should get a smaller carb, because your scooter needs to get up and go quickly. theres no point having a scooter that can go 200km/h but takes 5 minutes to reach that speed. however if you are driving longer distances and you have a lot of time between stops you can use a bigger carb to achievea higher top speed. how long are you prepared to wait for it?
another thing is engine rpm. if you install a bbk and use an original crank, that makes it more of a high rpm build. because the bore is bigger than the stroke the piston does not have to travel so far between revolutions. this means a higher rpm can be achieved and it can accelerate through that rpm faster. if you lighten the variator weights and use a bigger carb, this will allow you to rev higher and the time required for the engine to get up to its ideal flow velocity will be reduced.
for example
my stock 100cc yamaha engine came with a cvk24
it was pretty slow to reach a top speed and not very fast off the line. topped out around 95km/h
so i changed to a cvk30, big mistake on my part. i got an even slower start and only a little gain in top speed. 105km/h
then i upgraded the engine to 128cc. and it was faster off the line and had a much better top speed. something like 108km/h.
after that my friend (ex racing champion and racing bike builder) suggested i use a smaller carb and i was reluctant to at first. but after trying it on and a quick rip around the block..
it was like the beast had been set free finally and all the other mods i had made seemed to have finally paid off.
i took it out of the city and hit it hard!
KEHIN CVK26
it went off the clocks at 120km/h and kept going
i can only guess it topped out at 125km/h
so the moral of the story is, start small and work your way up. test as many sizes as you can before you buy one. i'm sure if you know someone with a keen interest in bikes they will have a few laying around that you can try out. if not then maybe a local junk yard can help you out
Read more: itistheride.boards.net/thread/7015/high-upjet-when-doing-bbk?page=1#ixzz3J1ngiaSq
