I'm working on a 2005 CRF250R. I bought this as a basket case project and am trying to figure out what I've got going on here. When I first got it, both valve keepers on the left intake valve had stripped and the valve dropped a little bit. Luckily it didn't hit anything, but it was enough that it had no compression when turning it over. Replaced all the keepers on the head and everything seemed to be great. Filled the ports with WD-40 and everything seemed to be sealing properly. Put the cam in the head on the bench to check all the valves and everything checked out ok. I was at .005" on the intake side, and .012" on the exhaust side. Pulled the cam and installed the head. Double checked everything as best as I could and put the rest of the bike together. Pulled it outside and fired 2nd kick. Rode it down the street a couple blocks and let it sit. Fired it back up and rode it down to the car wash with no issues on the way there or on the way home. Had a radiator leaking and a gas leak so pulled the bike apart to fix those. Let it sit for about a week waiting on parts. Got everything back together and went to start it, with no luck. Kicked for about 15 minutes before it lit, and noticed it seemed extremely hard to kick. If it was warm you could forget about starting it. Tonight I went out there, choke on and about 3 twists of the throttle and it fired after about 10 kicks. I knew it still wasn't right so I pulled the valve cover back off. Was double checking the valve clearances and noticed that the exhaust rocker wasn't even touching the decompression as it was turning. Pulled the rocker off and both shims were missing from the top of the exhaust valves. Luckily I found both of them before they did any damage but I'm puzzled as to what caused this. I'm wondering if I didn't knock them off before the cam was ever installed (bumped the exhaust rocker and they stuck to it or something) and it was just sheer luck that it fired when it did? When I put the shims back in tonight the valves were spot on what they were before. Just curious to hear if there's anything else I need to check, or if I just pulled a stupid? Thanks.