It's the 105cc 6.45HP engine correct?
I think you can swap it with any lifan 150cc (almsot twice the HP; 12.25 to be precise)
or loncin.. or whatever crosses your path that looks the same
Both engines mentioned above are Honda clones, they wouldn't last as long as a Honda, and they're not as well made, but they'll fit
The piranha 140cc looks like it'll fit, but I can't tell by the pictures if it IS a clone or not.
There are two Kits I think might fit..
a 132cc and a 146cc both for the lifan engine (the smaller 110 version)
But I'm not sure (that's why I don't link any

)
But: both are almost exactly as expensive as a 150cc lifan clone (~350 USD), so I don't know...
'sid