33mm is way too small. I put a 41mm on my 400 and it shot forwards.
we do an "easystart kit" for the round slides. we can put together the wear parts etc for the square slide but we tend to replace like-for-like.
we've never worked with a customer on the jetting on one of these as most people don't have the skill set.
so let's start with the shape of it?
you may have seen a thread about a needle I'm preparing for sale.
http://husaberg.org/fuel/24834-fe501e-2001-2003-performance-jetting-kit.html
It's going to be good.
Taffy