Don't use any lapping compound unless you are gonna tear down that engine. Pretty tough to insure that some doesn't go where it shouldn't. Lapping is usually done with a tool (power tool). There is an inexpensive method that looks like a dart that kids stick to windows, and it is run with a drill and lapping compound. If the carbon on the valve seats is not evenly distributed it tells be that there is a hot spot. Just a matter of time before she burns through if it is not addressed.