!!!!!!!!!!!! BE VERY CAREFUL WHEN MUCKING ABOUT WITH THE TIMING ON A 2-STROKE!!!!!!!
Thanks to the previous owner of my Merc I had a 3 pot rebore & 3 new pistons - if you advance the spark too far, when it starts there ends up being more fuel on the inlet side of the "piston dam" than the exhaust, which means when it sparks the bigger bang occurs on the inlet side and the piston is pushed sideways hard into the edge of the exhaust port..... The rest, as they say, is expensive.
Try the IanM approach first, and unless you really know what you are doing with spark settings, give it to a dealer!
I also guess it's a 2 cyl engine? They are very "lumpy" to pull generally. I manually started a Yam 55 2 cyl. It was like <brick wall> - <weeeee> - <brick wall> - <Wheeee> ... when pulled.