On 8/22/2010 7:15 PM, SF Man wrote:
On Sat, 21 Aug 2010 19:08:40 -0500, The Daring Dufas wrote:

All reciprocating (piston) engines are basically air pumps.

Ah. Now I understand what you're saying. Thanks for the details.

I tried blowing about 50psi compressed air into the spark plug hole ...
with mixed results (my compressor doesn't go higher than that).

- If the piston was at the top, it fluttered (see details below).
- If the piston was at another spot, it blew out the exhaust.
- If the piston was at yet another spot, it blew out the carbeurator.

But it never did run the thing (I think because of the pull-cord clutch
mechanism because it 'looked' like it wanted to spin but couldn't spin.
Probably because it wasn't fast enough to make the pull-cord clutch
disengage.

So, I think the "fluttering" was the piston trying to turn the crankshaft
but it couldn't because of the pull cord. I guess I could remove the pull
cord and test it without the pull-cord clutch...

If you'll look up how a two cycle engine works, you will understand
why the air came out where it did. The position of the piston is
what acts like the valves in a four cycle engine by uncovering the
intake port or the exhaust port. If the reed valve is good, there
shouldn't be any air coming out of the carburetor. Here's a link to
an animation that shows how a two stroke engine works:

http://science.howstuffworks.com/tra...wo-stroke2.htm

http://preview.tinyurl.com/33qdr5p

A bad reed valve could keep it from running on compressed air.

TDD