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Old October 26th 15, 04:03 PM posted to rec.crafts.metalworking
Cydrome Leader Cydrome Leader is offline
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First recorded activity by DIYBanter: Jul 2006
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Default Mount a 2 stroke upside down?

John B. wrote:
On Fri, 23 Oct 2015 16:50:45 +0000 (UTC), Cydrome Leader

John B. wrote:
On Thu, 22 Oct 2015 15:58:43 +0000 (UTC), Cydrome Leader

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?

Is rebuilding an engine really the easier option here? I just can't
imagine that it is.

I have a bike with an engine strapped on. It's a decade old Golden Eagle
kit with the drive ring and belt and a 25cc Redmax weed wacker engine. The
only engine problems have been gas tank leaks from that ethanol **** in
the gas. It starts in negative temps, or with old gas. Very solid little

It sounds like you're going for the engine mounted inside the triangle of
the frame and not something strapped over the rear wheel though. The fake
motorcycle style is all I see these days. Never come across another belt
drive bike like I have yet.

The "Whizzer" motor bicycle, and motor kits for bicycles, was made
from around 1939 until about 2009 and there are some NOS still

That's the style of kit I see in Chicago. I still prefer the leafblower
type as you just put a plastic bag over it and nobody knows it's a bike
with an engine.

Don't your "plastic bag" make a funny noise when you are driving?

The bag is for bringing it inside buildings where bikes are ok but not
other "vehicles".