94 xr600. I would probably not remove the valves myself, just take the head into the shop. Any idea what kind of money I am looing at for this and any other parts needed to put it all back together? The engine does have to come out to do this right? I have searched old threads and I think it is the guides. When I start it cold there is nothing for about 5 seconds then the smoke screen begins. Much more when I blip the throttle. It's gone in about 2 minutes and the bike doesn't use any oil. Is this guides for sure? I'd hate to do all the work and have it still not be fixed. When I bought the bike it did not do this the first 2 rides. Had always had bel ray semi sythetic in it but I couldn't find any so I used regular castrol 4t oil. Then it started smoking while cold. A guy I rode with told me his xr600 did the same thing when he tried non-synthetic oil but once he switched back it went away. I changed to the bel ray but there is still some smoke, although a lot less. I've thought about changing it one more time (since the first change couldn't have replaced all the non-synthetic that was in it) but have the feeling this is not going to fix it. The bike was bored, new piston, rockers in 02.