Impulse line?

[Scooterbum]

Where is it?And do all saws use one?
From what I gather it comes off of the crankcase.Does it run to the carb or to the fuel tank to pressurize it?
I know dumb question,but I'm used to 4-strokes. Thanks Steve

 

[blis]

the impulse line is between carburator and crankcase... Its job is to relay the pressure changes (vacuum/overpressure) to the fuel pump in carb. Thats what makes the carb´s in saws work in any given position..

And yes, all saws (modern saws) use it, thou in some it might be integrated to intake manifold, but generally its a thick black hose going from crankcase to carb...

 

[retoocs555]

On what saw?

Looking at your sig, you have mostly older saws. The impulse (vacume line from the case) on most of those comes straight through the manifold. If you've ever taken one of your carbs off and seen the intake gasket, that little hole that isn't for the carb bolts is to accomidate the impulse.