ucd
I just took an os91fx off of mine....and it WILL NOT go back on it.
I replaced it with a YS91 FZ.....WOWWWWWWW.Its a different plane all together. If you can afford it I would put the ys91 on it.
Some have had good success with a saito 100 as well. Both would be a good choice....On this plane a four stroke is the way to go...
next time you look at the UCD adds look at the 4 stroke muffler on the one thats hovering. The one the guy is holding one in his hands has a 2 stroke muffler....
Shane