The is a masterpiece of 1980s engineering—light, torquey, and timeless. But it is also a machine with unique quirks: a vacuum-operated petcock that fails silently, an RFVC head that hates incorrect valve lash, and wiring that turns brittle with age.
The GB250’s carb (Keihin VB31) is temperamental. The manual provides vacuum hose routing, pilot screw settings (1.5–2.0 turns out), and float height (12.5mm). Many online “fixes” contradict this data. Honda Gb250 Service Manual