I have a XR100r and a XR70r that are having the same issues.
The bikes start and run fine when not under full throttle or under a heavy load.
Today I pulled the Carb off the 70r and took it apart. I checked the jets, being that these bikes originally came from the mountains. Both jets we the factory numbered jets. I Cleaned them, along with the rest of the carburetor. I blew compressed air through all the ports and seen no blockage. I did notice that the hole in the slow jet was very tiny and I could hardly see light through it. I reassembled the carb and replaced the spark plug.
I cleaned the air filter also. The bike idles great but still will not rev great at WOT and under load.
I tried riding it with the choke partially on and the problem almost disappeared. This tells me that it is still a fuel / Carb issue.
Do any of you have any ideas? Do I need to soak this carb in cleaner over night? I took wire through all the ports and did not see any issues. Can the slow jet cause this issue or is it mainly for idling.