The MK0 has the same Doherty twist throttle that both of my MK1s have. The rubber grips are in great shape so I will use them. One problem I noticed awhile ago is that there is no adjustment for the cable which is about 3/8″ too long. Both ends have soldered balls so I did not want to cut the cable to shorten it. Both of my MK1s have replacement cables that I cut too length. So I had to turn the throttle maybe 1/4 turn before the throttle shaft would even move. With the twist throttle WFO I was getting only 3/4 throttle at the carb. The bike was plenty fast at 3/4 throttle so I did not mess with it.
I really wanted full throttle and I had noticed before that my 04-257 twist throttles looked a lot like the 1962 Doherty. I grabbed one and soon realized they are almost identical except for the rubbers and the adjuster on the 04-257.
I removed the adjuster and compared it to the old Doherty. Turns out all I have to do is tap the old casting and then I can fit the adjuster to the original throttle. So I measured the threads and found that they are M9 x 1.25. I have a fairly complete metric tap set: M6, M7, M8, M10, M12, M14 and M16 in fine and coarse pitches. I do not have a M9 x 1.25…… So I now have one ordered.
Of course I am annoyed but now I decided to find out just how similar the new and old throttles are. Turns out they are interchangeable with some minor deburring. I installed the lower adjustable piece on the old Doherty top piece and it fit.
This will work until my new M9 x 1.25 tap shows up. The adjuster now allows me to get full throttle on the scooter.