How many times have you had your bike not run 100%. Well, if you ride a XR100 it's probably quite a lot (like every race). I always tend to blame jetting; (if you have points, always blame it on the points, but I'm running a CDI) -- if it would miss in the middle and I would change the clip on the needle or adjust the air screw. I would try every main jet, clip position combination possible and usually to no avail. Anybody who has been through this knows the frustration. Anyway, My bike has been running like asthmatic dog for about two months. I recently had to do some emergency head work after a bent valve, so I thought this might cause the jetting to be off, and even before that it never would idle properly. So the first thing I did was to buy a new carb kit, I actually only wanted an O-ring, but they only come in rebuild kits. This seemed like a logical step, because if your bike doesn't idle smooth there's a good chance there's an air leak, but after installing all new O-rings, the bike ran the same. So step two, I bought a new carb, drastic, but sometimes you have to just replace old friends. This fixed the idle problem, but not the midrange blubbering. Then, Chris and Dan Alamengos and I were out riding at Elsinore, I had Chris ride it and he deduced that since the blubbering was intermittent, it was either electrical or a dirty carb. So he cleaned the carb and I clean all the grounds, we threw it back together and I took for a moto. I couldn't believe the difference; it was a rocket ship. It ran smooth all the way from the bottom to top and revved to the moon. Now, I don't know if it was the dirty carb or the ground, but the bottom line is never stick to one mindset, it just might closed your mind to other possible solutions.
It's not always Jetting