The results of valves adjusted too tight will be difficulty getting the motor to idle, low power and low manifold vacuum.

As far as a grade of oil, it's hard to beat a good multi-grade oil like 10W30. The "W" stands for winter, so in cold weather it acts like a thinner oil, yet protects in hotter weather like a 30 weight.

If your oil is black, it's probably due to the molybdenum disulphide that you used as a break-in lube. It is black as the hubs of hell.