
My 450 was 456cc, 11.5:1, with an aluminium flywheel, but if done with purpose it would start with one or two trys. Setting the lever up on the splines so that you can get a full swing, and following it through for the full spin helps a lot.
If all else fails then this advice can help.
http://www.youtube.com/watch?v=cY1YndLmbXQ