I bought this TBI 350 out of a '95 Tahoe to drop in my project. Owner said it was running when it was pulled (truck was wrecked). I figured I would inspect it before I dropped in in just for good measure. There are large amounts of carbon deposits on all of the piston heads and the valves. Also on the #2 cylinder there is a small amount of surface rust twards the top of the stroke. My question is what could have caused the carbon build up in the cylinders, and what should I do about the rust? Any info would be great!