I just brought the wr300 home last Monday

and it ran like shite. Old, maybe cheap, gas was part of the prob, but also lean on top and blubbering and spooging in the middle. After checking all the basics I did 2 20 mile rides, so @ 2 gallon of fresh 100% gas w/50:1 Interceptor. That helped a little, it starts pretty easy, smokes a little and was still blubbering through the middle in every gear and spooging all over.
First thing was to order some jets and gaskets. I didn't want to spend $100 on the JD kit because I plan to replace the carb in a month or 2 and thought with all the info here I could get the Mik to work for now. I ordered the 6sigma jet kit (@ $40) for my bike and altitude and that's done the trick for my altitude and temps, though I'll probably lean it out some more when the cold weather sets in.
I ordered 2 cr250 reed block gaskets from the local Honda dealer also and installed them on either side of the reed block after cleaning it all up really well.
I'm 2nd owner, the bike had less than 10 hrs on it and carb was stock. It was set up by a BMW dealer in Raleigh, so low elevation. I'm riding at 2000-4000' , fast fire roads and greenways, steep hills and single track.
I found the carb had 420 mj, 45 pj, GAY needle 3rd slot and that the float was @ 18mm. I adjusted the float to @ 14mm, 6sigma sent a 37.5 pj and I went to 450 mj and left the needle as is, AS is @ 1 1/4 out. That helped a lot, no more spooge!, but 1st-3rd was still blubbering in the middle. Then I moved the NJ clip to slot 2 and that's cleaned up the middle pretty well. It still needs some fine tuning, but at least it's rideable and doesn't puke fuel when on the kickstand.
The other noticeable change is the starting ritual. Cold, I was leaning the bike until it pukes gas, full choke, no throttle, kick a few times, wait, kick it hard and it would start and idle. Warm, it would start 1 kick with no throttle. Now that it's leaned out on the PJ and needle I still lean it 'til it pukes, full choke, and give it throttle as I kick, starts 1st kick cold and warm (with no choke).
Do note that float level is critical, especially with a rich MJ. If the float level is low and you run WOT the engine can starve and seize!
The 6sigma kit included:
3 MJs;
1 PJ;
2 NJ shims (1/2 clip step);
1 nylon spacer;
a drill bit and removal screw for those with sealed AS;
and 10 pages of instructions with pics.
chees