Just put on a Mikuni TM40. Oh my god. This carburetor fixes everything wrong with this bike. I have a quick tuning question.
When I first started my bike with the Mikuni it took a long time to warm up and let me touch the throttle even though it was 65F outside. The second I barely cracked the throttle the motor would die. It seemed to run way better on the choke until it got warm and then all of a sudden I could start to rev it like normal.
First though? Pilot is too lean. Well, my theory was wrong. It ran way worse with the pilot richened up 1/4 turn. It actually responded better with the pilot leaned out a 1/4 turn from stock (idle revs went up, responded better to quick blips of the throttle).
Now unfortunately my battery was dead from sitting and I think I was experiencing problems because I didn't have strong enough ignition until the battery charged up a bit....I think...
However, I have a slight hesitation when I barely crack the throttle open and hold it open at like 1/32th opening. It might be because of the way I tuned the accelerator pump. I adjusted it so the lever is about 1mm away from touching at idle, so it takes about 1mm of throttle opening before it actuates. From the factory the lever was actually touching at idle and I didn't think it should be that way but I don't know.
BTW, this carb came prejetted from power-barn specifically for the XR650R, but I'm not sure what is in it because I didn't crack anything open and take a look and they don't list it. Other than those two very minor problems this carb rips! It's perfect! It's hard to keep the front end on the ground!!!
I live at under 1,000ft ASL, it was 65F, I have a K&N filter (which I want to replace with a UNI), fully uncorked, White Brothers E2, emissions stuff removed, still stock on everything else though.