I am the mom of a 14 year old son that rides an 03 RM 125. The engine was completely rebuilt recently - about 12-15 hours on the bike since the rebuild (done by a professional). We bought the bike just before the rebuild... and it appears to have been very well taken care of by the previous owner. Currently, we are at an elevation of 4300 ft, (we usually ride at 500-1500ft) and the bike starts first kick and runs beautifully. Until you turn it off. Then it takes several hours to be able to start it up again. It won't even bump start. We've replaced the spark plug and checked that it is getting a spark. The air filter is clean. The gas is new - premium, 40:1. The carb outlet tubes are clear, no blockage. Could it have anything to do with the elevation change? This is our first year with the 125, and never had any trouble with the RM 85L we had. What things can I check myself...with my limited knowledge? I am a mom...not a mechanic, but I am learning and don't mind getting my hands dirty! There is no male mechanic in the picture (aka dad), so it's up to me to figure this out. I'd love any advice you had to offer, just remember I am a true newbie PS. My son's friend is on the trip with us and he has a Kx 85 that won't start at all. Being on a trip with two teenage boys who can't ride, while surrounded by dirt trails, really sucks! Lol!