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West Wight Potter Mailing List maintainer
dfarrell@ridgecrest.ca.us
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>The crankshaft is used to take the motion of the piston and rod and convert
>it to a cercular motion to drive the prop.
Thanks for clarifying that, but I don't think anyone was disputing that :-P
>the crankcase on the otherhand is
>under presure when the piston comes down and vacume as the piston goes up.
on a 2-stroke, yeah, as SF pointed out. I was thinking 4-stroke earlier, and
every 4-stroke engine I've ever owned has been generally under crankcase pressure.
Now that I think about it though, i suppose a 1-cylinder 4-stroke might create
a little crankcase vaccuum on the compression and exhaust strokes, since theres
no other cylinder on a power or intake stroke to cancel the volume displaced
by the moving piston.
I had forgotten about the pumping action of the crankcase in a 2-stroke. The
vacuum there certainly could drive a fuel pump. But I just never noticed having
a fuel pump on my tohatsu, and the owner's manual does not speak to a fuel pump,
nor can I find replacement pump parts in any of the online sources. If there
is one, i'm sure its in there somewhere (maybe integral to the carb?). I had
just always assumed that the venturi in the carb would be enough to suck the
small amounts of fuel used by a small outboard up the short fuel hose. Does
anyone here have an actual service manual for one of these small outboards (specifically
the Tohatsu/Nissan) that tells for sure?
The upshot of all this is, of course, that if these small outboards don't require
a fuel pump, whoever wanted to try using an external tank may be able to do
so with some simple fittings.
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