Choke / cold-start enricher

How it works

The choke (or enrichener) helps a cold engine start. When the engine is cold, fuel vaporises poorly and some condenses on the walls, so a richer mixture is needed. On a carburettor bike, a lever on the bars or a knob opens an enrichment circuit (or closes an air flap); on some bikes enrichment is automatic, controlled by temperature. On a fuel-injected bike, the ECU enriches the mixture and raises the idle by itself. A choke that no longer opens makes cold starts very hard. Conversely, a choke that stays on (sticking cable, stuck plunger) makes the engine run too rich once warm: high idle, black smoke, fouled plugs and higher consumption. The choke cable must slide freely and the lever return to the off position. Close the choke gradually as soon as the engine will run on its own.

Maintenance tips

• ✓Close the choke gradually as soon as the engine holds idle, usually after a few tens of seconds to a few minutes.
• ✓If idle stays high with the engine warm, check the choke has fully returned to off.
• ✓Lubricate the choke cable and check it has a little slack at rest.
• ✓Very hard cold starts: check the choke really opens at the carburettor before looking further.
• ✓Don't warm the engine up for long at a standstill on choke: ride off gently once it holds idle.