valve guides
 

My 1988 xt600 smokes on startup after being idle for about a week. I am thinking its the valve guides, the bike has 18000 miles, should I worry about it? Thanks Albert

Oils deffo getting into your cylinder but very slowly. Could be the vavle stem guides (most likely) or head gasket.

Its not going to harm your bike but its worth doing. valve stem guides are cheap and easy to fit with a half decent mechanical mind. A bike shop should do the whole job in an hour.

If it only smokes after it has been sitting for a while, could it be wet sumping?

Actually I don't know if these engines ever have that problem but if this happened the engine would burn a bit of oil until the oil pump returned the excess oil to the tank.