When the engine is hot, fuel vaporises faster. If your mixture screws or float heights are even slightly off, or the carbs are dirty inside, the air/fuel ratio can become overly rich. This floods the engine when hot and makes restarting difficult. Another common issue is leaking float needles or perished O-rings, which allow fuel to seep into the intake while the bike is sitting, effectively drowning the cylinders.

Worn choke plungers or sticking choke cables can also contribute, as they fail to fully close and leave the enrichment circuit open. This keeps feeding fuel even when you don’t want it.

At The Carb Shack, we see this issue frequently on bikes that have been “rebuilt” at home but never bench tested or ultrasonically cleaned. Our process removes every trace of fuel varnish, replaces float needles and O-rings, and resets mixture screws and float heights to exact specification. We also test the choke system to make sure it’s closing fully.

If your bike starts cold but refuses when warm, don’t keep cranking and risking damage. Book a carb clean and rebuild service with The Carb Shack and fix the problem properly.