Well last year I did not get a chance to ride. This year I am hoping that will change! The OEM parts were replaced with Pro X pistons and valves. I am wondering if maybe jetting would need to be changed because of this? Maybe a different dome on the piston or some change in the valves? My thoughts, when cold the bike starts easily with just choke. It still becomes difficult to start at times (not all the time). I have typically run with a silent insert in the stock exhaust to make it friendly around town. When I put this in the bike runs like crap, remove it and it pulls hard (not as good as it did before the rebuild). My thought is that with changes from OEM to the Pro X I may need to lean it back out a bit. Anyone have a Pro X set up running at 1500'? Jetting? Check the normal culprits, plastic hot start nut for a crack, seal, replace the pilot jet, set the fuel screw. Pro X parts should make no difference.