Xr100r (120cc) no top end power?

Got the tb 120 for the ol' 100, a atc200x carb and fmf powercore4. After the rejet runs great... Awesome low end but she falls right on her face after like 5k??? It can hold full throttle fine but once she gets some r's its game over... Sputter sputter:( Im thinkin she has asthma and cant breathe, cause the tiny valves and stock cam.

You guys think a cam would do the trick or is it somthing else.

What jetting are you running?

128 i think main 40 pilot ill check when i get home.... And I'm at sea level. South fl. Hot as hell mid summer

Feels like its suffocating.... Making it run rich? Plenty of low torque but nothing on top.

Bigger carb on an engine doesn't prevent it from running at higher rpms.  Stock cam and valves have nothing to do with your problem, it ran at high rpms with the smaller stock carb!  So you have a problem with your swap.  More than likely jetting, but could be clogged fuel system not allowing enough gas to get through or something else simple.  Make sure your choke is working correctly and start playing with jets and moving your needle up and down to see what effect it has on the problems.  Make sure your filter is clean/lubed and flowing well.  Make sure your exhaust is un-obstructed and free flowing.

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