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need help to pick out the right carb size

880 Views 4 Replies 3 Participants Last post by  jaguar
im putting a big valve head on my 74 CB125s. dont know if i need to run a bigger carb. the valves are 2.5mm bigger. plan to run with no filter. rest of the motor is stock for now but i am looking for a high compression piston. what size carb do you guys think that i need? aslo what size is stock?
i saw that the ecta record in the 125 four stroke is only 65ish MPH. think that my cafe will do more then that!!! wanted to go and thats why im doin the big valve head and not the bore kit
thanks for any help

There is the right way, the wrong way and the british way to do anything!
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should i run a 28mm?

There is the right way, the wrong way and the british way to do anything!
You may be better off trying to work with the stock carb. What are you doing for an exhaust? I found that with my XR100, even with a performance exhaust and K&N filter I only had to go up 1 size on the main jet.
Having said that, when I look at the performance mods for the XR100, you can get a 24mm flatslide for it, suggested if you do the 120cc kit. I can't remember what the stock CB carb is. I'll look in the barn later this week and see if the XR carb is similar to the CB carb.
You can also have your CB carb bored out, which would save you from modifying the mount.

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