A cold underbone needs thirty seconds of kindness. The technique differs slightly between carburettor and fuel-injected models — our carburettor versus fuel-injection guide explains the systems — but the habit is the same everywhere.
Carburettor models: the choke
Older and cheaper underbones mix fuel mechanically, and a cold engine needs a richer mixture to fire cleanly. The choke lever (usually on the carburettor body or the handlebar) enriches that mixture for starting. The routine:
- Fuel tap on (if the model has a manual one), choke on.
- Start the engine — electric button or kick lever; the kick-versus-electric guide covers both.
- Let it idle. A cold idle will be slightly fast and rough for a few moments.
- Push the choke off as soon as the idle settles — usually within a minute. Riding with the choke on wastes fuel and fouls plugs.
Fuel-injected models: no choke
Modern fuel-injected underbones (most current Honda and Yamaha models) measure cold-start fuelling automatically: turn the key, press the button, ride away gently. No choke exists, and holding the throttle open while starting can actually confuse the system — cold-start with a closed throttle.
Warm-up reality
Thirty seconds to a couple of minutes of gentle riding warms an underbone better than prolonged idling. The practical rule: easy throttle, low gears, no full-throttle launches until the engine feels smooth.
When cold starting goes wrong
An engine that will not fire when cold but runs fine warm usually points to fuelling; one that stalls when hot has its own failure pattern covered in the hot-stalling guide. A bike that will not turn over at all is usually the battery — the overnight battery drain article covers the first checks. Rental riders: report starting trouble to the rental provider rather than experimenting, and confirm availability and condition when you pick up.