ORIGINAL: j.duncker
Your wooden prop was lighter thus having less flywheel effect. When the engine fired there was insufficient stored energy to carry it over the the next compression stroke and it kicked back reversing the rotation.
NB Lots of people make use of this quirk and by flicking the engine BACKWARDS get it to start running forwards.
What he said,, You can use a heavy spinner to help you out if you are not use to running
a low rotational mass. This will slow down your spool up time but if you are not 3Ding it does not matter.
cheers Tim