MM, but could see this with others

[PTmowerMech]

How can a Stihl engine start and run fine, when the primer bulb doesn't stay full. In fact, when priming it, it'll suck fuel into the bulb. But once you crank it, it sucks it right out.

From what I know, the primer is only there to suck the air out of the carb and prime the cylinder. But in almost all cases, when everything is fine & dandy, the primer bulb never looses it's prime, when it's running? Is that because it's got no place to go, because of a check valve? Or because fuel is constantly being pushed into the primer when it's running?

 

[Hammermechanicman]

After the purge bulb purges the air from the metering chamber it doesn't do anything. With the engine running it doesn't need to have fuel in it. Fuel does drain out sometimes when it runs