[Okierider]

Well I have gone back to the factory Youall carb.
Using stock jetting on the youall a 125 jet is running rich for me. Last ride I had it on (around 50 miles driving it to our new house) it would start to drown above 9000 rpm.
The Mikuni is a better carb for a lot of reasons, but primarily due to its ease of tuning. Once you’ve got the pilot circuit figured out you never need to remove the bowl again. Swapping mains only requires removing a nut at the bottom of the bowl. It is an exceptional piece of machinery, truly.
However, I came to realize that I was fighting not with jets but with the needle profile and slide cutaway. Mikuni slides (from what I’ve gathered) come with cutouts numbered from 1 to 2.5 in .5 segments (for the vm28 anyway). The carb comes jetted 60/200 pilot/main and has an appropriately sized cutaway (2.5) and needle (5P21) for that size jetting-way, WAY too large for the 250. In fact according to the Mikuni VM tuning manual 28mm is at the bleeding edge of being too large for a 20hp 250-26mm is what they would say is appropriate I think. Then you have to figure out a needle profile. 5 or 6 step, and a dozen different needles makes it a pain for a noob.
The stock carb has a much smaller cutaway and a much thinner needle profile than the Mikuni and that made a world of difference in consistency.
It is slower, but we’re talking 2-3mph at the absolute top of the RPM range in 5th gear-however the heat may very well account for that.
I have a 26 floating around that I may try in the future (it’s much smaller than the youall) but for now it’s fine lol.