I just bought a 2004 kx250f. He said the engine/valves were all just rebuilt. It was a little hard to kick start, took some getting use to after riding a 2 stroke. But when i would get it top dead center then kick it usually worked fine. But about a 1 hour/1 1/2 into my first time out riding it it was getting hard to start and had to push start it. Alot of times when I slowed down it would die. But compression wasn't that bad and road fine when it was going. After I got home and the next weekend I was getting ready to go ride I wanted to make sure it would start and there was no compression. Now I can't kick start it, only push start it. I checked everything but cannot figure out what it is. When we kicked no air sucked in the exhuast and no air blew out of the carb. took oil fill plug out kicked it with thumb over hole to see if there was blow by air from the piston and there was not excessive pressure. Carbs were cleaned out good. Disconnected air box from filter in case it wasnt gettin enough air. I called the guy i bought it from, told him whats up, he three wayed his mechanic, we went through all the same steps we checked. he called some buddies and they said that since the engine was rebuilt and i took it out it broke in the engine and now it set. So to do a valve adjustment/shim. Does that sound right ande what do i need to do to get back out riding? Regards chris.