On Mon, 26 Oct 2015 14:06:48 -0700, wrote:

On Sun, 25 Oct 2015 07:38:24 +0000, Charlie+ wrote:

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

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

I just wonder if the ignition in a point-less system will work so well
if the flywheel rotation is reversed? With the points type magneto it
makes no difference but with the pointless type the system is optimised
with a mapped timed firing by potted electronic components built into
the coil assembly (hence the modern easy start 2-stroke systems) and the
coil can be much smaller and cheaper as the UHV is generated by
electronic circuitry rather than directly by the magneto. So- maybe the
mapping will not make the corrections in the right direction etc.? I
would anyway try running it in reverse with an electric drill etc. to
see how the ignition might work if you do this?! Just a thaught - I
havnt tried so absolutely no actual experience with running this type of
ignition in reverse, someone else here might have?! C+
Thanks for the reply Charlie. It would be a good idea to see when the
spark occurs. If, for example, it happens at 12 degrees before TDC
then I need to make sure it happens on the other side of TDC since the
crankshaft will be spinning the other way. Using a drill to spin the
engine so I can watch the spark timing is a good idea. The electronics
for the ignition are located away from the engine, it appears that the
magneto coil is only a coil and has no device for sensing crankshaft
position, so all the timing is done in the black box that is mounted
away from the engine. But I still need to see what the timing is to
make sure I get it right when reversing the engine.
Eric

Many of the very simple old 2-strokes just relied on the magnet
*leaving* the field to time the spark. Sort of time, that is. g As
the motor speeds up, the spark timing actually can advance a few
degrees that way.

You may be able to tell from the relative position of the magnet in
the flywheel, to the magneto coil, where the timing is. In any case,
it will give you guidance about setting it on the opposite side of TDC
if you want to run the motor in reverse.

--
Ed Huntress