Good job on the 250 YZ Romeo. I like the twist grip throttle, looks like a nice setup. You probably had to change the porting on this engine to get the top rpm wailing ?
As you can see here is my 1982 YZ 125.I built this saw in 1984. Notice the black cable running from under the carb, thats the pressurized chain oil tanks control cable connected to the throttle. I got a Schrader blow gun screwed into the bottom of the oil tank piped into the bar pad.The cable is connected to the gun lever, oil releases around 3/4 throttle. Thats a .050 General guide bar on it [made in Tigard Oregon].General made beautiful bars. The long bar on the ground is a Cannon. The chain on the saw is only a practice round filed chain, lol .
You notice the box of files in front of the saw? Thats a full dozen of brand new Windsor chisel bit files [ probably the last dozen in the world] Last of the true edge files. Beautiful file to file with. This saw weighs 42 lbs ,it still needs a major weight reduction. Going to try a new pipe and a newer carb. Thats a 42mm HD on there now. Good project for next winter.Saw was built for cutting 10 inch x 10 inch spruce logs. Times in the late 1980s ; hands on log ,cold start ,3 cuts all down [ no up cut allowed ] within 6" of log in late 4 sec. low 5 sec. time.