This is an ongoing conversation, da Rock is correct the engine does not know up from down, when it is running...

The trick is to GET it running! [:'(]

As the fuel comes into the cylinder it tends to pool in the head which 'cools' the glow plug and may starting hard, SO... a hotter glow plug may be needed and most definately your tuning has to be very good (not too rich) to prevent the pooling. Also, when inverted the position of the fuel tank is important, as the carb is now lower the tank may have to be lowered to prevent siphoning.

Once you correct these little problems the engine should work like a charm! If you don't like this much work but still don't want a verticle engine, try mounting the engine at 90 degrees...