Just picked this 543xp clone up, a couple of coworkers had good luck with a couple of Farmertec 440s I helped them build(I did have to do some machine work to the cylinders and put a chamfer on the port edges,) so I figured I couldn't go wrong with this. The plan is to throw it on the front of the dirt bike, for times when one of my top handles is going to be too small.
The verdict so far...it starts and kinda runs. Metering rod was way out of adjustment on the carb, even after fixing that, it still runs like doo doo. Feels like a timing issue, the way it pops in the cut. I could just send it back, but I'm going to do a tear down on it anyway, so I'll try to get it right. If it's not catastrophically a piece of crap, I'll do some port and machine work on it, in order to pick up some grunt.
In case any of the haters pop up, while a genuine 543xp would've been the turnkey option, I'm not spending $600 on one just for it to bounce around on the front of my dirtbike. I feel bad enough doing that with my 2511 or my 201tcm. My 2511 gets abused harder on trail cutting days than it does on the average day of tree climbing.