Did you follow any of Norms tips prior to running you motor? I read up on the forum here, to look for common problems with these little motors- my biggest issue with my early builds were air leaks, intake manifold gasket gave me trouble- leaking Head gasket can make "em hard to start...... These are some places to start-do you have any leaks at the head, look for seepage above the intake all the way round the head.
any more details on what kind of problem?
-Richard.