Hi!!

Do you you mean when the engine is mounted inverted(upside down)??
If that is the case, you must be carefull not to flood the engine. Applying the starter to a flooded inverted engine could result in serious internal damage.

When I start mine I don`t prime the engine at all and just open the throttle to just a little over idlespeed.
With the glowstarter attached I crank the engine while blocking the exhaustpipe for 1-2 seconds. It will usually start after a few seconds.

Hope this helps!

Flyby