I have the same issue with my 2 stroke speedster...some times running in reverse frees it up and it runs great for the rest of the day....last time out after an hour of revving great in reverse, and bogging down going forward I gave up.
I love the boat when she's running right, but this is sad...some people mentioned the oil thing, but why free up for the day once it breaks loose?
I thought it might need a new pump....
Still wondering...