On Fri, 23 Oct 2015 12:54:23 -0700, wrote:

On Thu, 22 Oct 2015 09:03:57 -0400, Ed Huntress
wrote:

On Thu, 22 Oct 2015 00:00:13 -0500, Tim Wescott
wrote:

On Thu, 22 Oct 2015 08:53:44 +0700, John B. wrote:

On Wed, 21 Oct 2015 14:01:25 -0700, wrote:

Because of the size and the way my bicycle frame is shaped it may be
more convenient, strictly from a mechanical point of view, to mount a 2
stroke bicycle engine upside down. Maybe upside down and backward. If I
did this the carb would need to be inverted because it is a float bowl
type carb. I suppose I could use a pumper type carb instead but I don't
know if I have one that is suitable as far as fuel and air flow are
concerned. Besides, small engine pumper carbs tend to be kind of on/off
devices in that they idle OK and and run wide open well but don't do so
well in the mid range throttle settings. I suppose I could buy one but
I'm cheap. So, if there is room to invert the carb what else do I need
to worry about? Will the crankcase tend to get too hot since it will now
be above the cylinder? And lets say that the engine is not only inverted
but also turned around. Now the engine will be rotating the wrong way to
drive the bike forward. Since the engine is a two stroke it seems to me
that I will only need to change the ignition timing. I think this can be
done simply by broaching a new keyway in the spinning magnet flywheel.
The ignition is a fully electronic CDI type with no points. I assume the
ignition works by sensing the voltage rise in the magneto primary
winding as there is no other provision for detecting the position of the
flywheel magnet. Have I missed anything?
Thanks,
Eric

Model airplane 2 stroke motors are frequently mounted upside down and
run all right although if you flood one it might be a bit more difficult
to start and chainsaw run all right upside down.

As for running backward, I'm not sure of the efficiency as some modern 2
strokes use some pretty exotic porting that may be rotation directional
in nature. I'm leaning on model engine experience but some glow plug
designs of model engines seemed to run in either direction with no
problems and other, different in design, wouldn't seem to run backwards
at all.

The rotation direction thing is what Ed was referring to -- most model
airplane 2-strokes have intake ports that are timed by the crank, and
that lead the piston by a considerable amount. This makes the engine
prefer to run in just one direction. Cox reed-valve engines are
direction agnostic, as are the really old piston-timed engines.

I'd really like to see the engine the OP is talking about. Chances are
that it's a piston-port engine, as most bike motors have been since
the beginning. My old O&R bike motor is a cross-scavenge, piston-port
engine -- the basic 2-stroke design that powered everything including
lawnmowers and ancient washing machines, and was used in all sorts of
applications where you're after low cost and smooth running, rather
than performance.


Weed-whacker and chainsaw motors are, to my knowledge, piston timed, with
the intake port to the crankshaft opened and closed by the skirt of the
piston rather than by the crank or a rotor attached to the crank. So,
they'll run pretty much the same in either direction, once you get the
spark timing sorted out.

I think that both piston-port and reed-valve intake have both been
used in chainsaws. Either one will allow an engine to run in either
direction, given the ignition timing issue discussed before.
ED-the engine is piston ported. These engines are ubiquitous online. I
know they are not all made in the same factories but they are all
similar. See the link:
www.californiamotorbikes.com

Aha. Yes, your basic piston-port 2-stroke.

I had, years and years ago, a Yamaha 80 that used the rotarty valve
setup. It was interesting because the carb was inside the engine case
on the right side. I think Kawasaki made a similar engine. Also
interesting was the fact that there was a Honda motorcycle that not
only looked a whole lot like the Yamaha but had some parts that were
interchangeable. Like the front forks. These weren't the telescoping
type forks so to swap forks the whole front end needed to be changed.
Eric

There sure were a lot of oddities in those early Japanese bikes. They
were pretty clever.

--
Ed Huntress