[AT] OT McCullogh chain saw parts

[Steve W.]

charliehill wrote:
> Yes it pretty well has to be vented to some degree to keep the presure 
> somewhat constant.  Luckily this 30 year old McCulloch is built a little 
> better and uses a little less plastic that some of the stuff out now.
> 
> Do you remember how the old 2 stroke dirt bikes  had a plastic tube run 
> through the center of the gas cap?  I always figured it was some sort of 
> vent line but I never owned one so I don't know.
> 
> Charlie

Depending on the model it could be a J tube vent or a S tube. They
allowed the fuel to slosh around and move without giving you a bath. A
street bike has a vent in the cap (like any tractor) to allow fuel to flow.
The tube runs from the tank down to a small catch can which is also
vented directly.

On the chainsaw the vent basically is a one way flap. It allows air in
to keep fuel flowing but shuts to keep gas from coming out. Most of them
also have a sintered brass filter over them to keep crud out, others
have simple screens. Your oil cap also has a vent.
Both gas and oil are pumped and as such the level dropping creates a
slight vacuum in the tanks, without the vents it can stop fuel/oil flow.
Not a good thing.

-- 
Steve W.
Near Cooperstown, New York