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

It sounds goods. Most 2-strokes don't care if they run forward or
backward, as long as the ignition timing is adjusted.

If you showed us your engine, I didn't see it. One exception about
running backwards is if the engine has a rotary intake valve mounted
on the crankshaft. That's been used on some old off-road motorcycle
engines and some other high-performance types, but it's very unlikely
on most other applications. I'm guessing your engine doesn't have
pump/squirt lubrication, which is another limitation on running
backwards.

Lots of 2-strokes run upside-down. As you say, it's a matter of
whether the carb has a float bowl and which way it thinks is "up."

--
Ed Huntress