The bike runs now. Actually, it ran last week. The magic ingredient? The fuel tank.
I tested out my newly refreshed CDI box on a second bike, and it ran fine. The CDI refresh was done by Carmo in the Netherlands, seemingly the only place in the world doing this work. Came home and no luck. So… What was different? The only difference between the two bikes was that the other one had the tank mounted and hooked up. Something so simple……
This is important because attached to the fuel tank is a vacuum petcock, and the hoses that operate it.
While I’d been careful to close off the vacuum port on the side of the intake that opens the petcock, I hadn’t closed off the fuel feed line to the carb. So I was either running out of vacuum, or running out of vacuum. The Mikuni carb is a constant-vacuum type and requires militant fastidiousness when it comes to policing the vacuum lines. I’ve honestly never seen anything like this. Even my poor old Passat will fire and run with some vac lines open, being a modern Bosch innovation. My Rabbit would run with most of the intake missing, and it was merely K-Jet. Perfection, I tell you!
Since getting it running, I’ve also rejetted the carb, going up one size each on the main and pilot jets to #130 and #20 from #127.5 and #19. I’ve found references to this pair, and also to simply moving the pilot jet up to a #30 while keeping the stock #127.5 for the main. I expect my summer to involve a fair amount of carb tuning and experimentation – which will be great because it will put me in a much better position to handle little Japanese bikes in the future, and hopefully prepare me for a future life of Bing.
Yeah. I’m going there. Two Bings, to be exact.