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i have an 2000 honda xr100r. it is bored out to 120cc. the valves, cam, and carb are stock. the stock carb is 26mm. im thinking of buying a 30mm carb for it, would it be too much for it? and would it give it a noticable ammount of more power?
 

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i have an 2000 honda xr100r. it is bored out to 120cc. the valves, cam, and carb are stock. the stock carb is 26mm. im thinking of buying a 30mm carb for it, would it be too much for it? and would it give it a noticable ammount of more power?

Considering the '05 model lists a 22mm carb I'd be inclined to think a 30mm might be too much for it.
Looking at Wiki it appears the XR125L puts out 11hp (I assume at the crank) so I'd guess the 100 is something around 8-9hp. The extra 20cc you have probably pushes it over 10hp. A good exhaust system might get you another 1-2hp and a good camshaft might be good for another 1-2hp. That should give you similar power to a well-tuned but essentially stock XR125.
Is that going to be "noticeable" though?
For me, probably not, it's still only a 120cc four-stroke single.
If it's the only bike you've ever ridden though it might liven it up a bit.
 

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what about a 27mm? or 26mm? i thought the stock was 26mm, but i looked it up and its 22mm

I would go with a good cam before a bigger carb.
 

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Four strokes are fickle if you just fit on too big of a carb it looses a lot of the lower end torque.
Add it to a small displacement engine with modest horsepower/torque and you risk loosing it all.
As Blade suggests get an aftermarket cam, but buy one that has a performance profile suited to your needs and an exhaust system to match.
Once those items are on the bike and its re-jetted, only then will you know its potential.
You could then try a carb rejetted from the 125 model after your updates just to see if any improvements are noticable.
 
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