Burnt Valve Question

Before I go taking off the head of this 1.0L Metro engine I'd like to know
how a burnt valve acts in relation to the performance of the engine. What it
is doing is acting like a bad miss. Like it even has water in the gas. It
sputters and misses when it's under load [like climbing a hill or
mountain]. On straight roads when the load is reduced it straightens out
and runs well. I'm going to do a compression check here in a little bit and
also change the plugs, wires and distributor cap before I get into the
head. We just bought this thing knowing it has a problem and the seller
seems to think he burned a valve. It also produces a puff of oil related
smoke out of the exhaust just after you start it [cold] and put it into
gear. It quickly goes away when shifting out of 1st and doesn't come back
again until it cools off and restarts.