I don't think the "gear oil" is helping you any. When you say gear oil, must of us think of 90 wt. If that is the case, there are oils made just for air filters and they do a great job.
Back in the 70's we used motor oil, most the time I selected a light wt oil. The heavier wt. oils do not pass as much air thus you could run VERY rich. If the jets are all clean and all passages in the carb. are not blocked, you should get reasonable running conditions with stock settings.
Those little bikes would run at just about any altitude and only minor adjustments were needed.
Points..I think it has electronic ignition. Needle worn...maybe, but I've NEVER seen anyone wear out a needle on the XR 100's. A friend of mine had the exact problem. It took about 3 times to get the pilot jet, (some call it idle jet) clear. The passage is VERY small. Don't cram a drill bit through it. It will end up too big and not run right.
Has it ever run properly since you have owned it?
Also...I may be wrong,(someone out there help me) but on those bikes turning in the screw leans the mixture, just the oppisite of a 2-stroke. It is a fuel mixture screw where-as on 2-srokes it is an air mixture screw. So turning in the screw reduces the amount of fuel not air..that would explian why it runs faster.
The running condition you describe sounds like the choke is on! It most likely starts easy if that is the case.
Hope I have helped.