Now see, you didn't say you were using new guides! This means the whole process you have started is to be done again and with more work to be correct. You will need to insert the guide into the bore by itself and ream it to fit the valve stem. Are the valves new? This is where at least half of the wear is in the train.Next, the valves will have to be put in with the guide in place and the valves lapped in place to insure the seat is concentric and the valve contacts all the way around and in the middle of the valve seat. You talk about lapping the valves and replacing the guides with lapping in the context of being the first process. This won't work. The valves have to be lapped, in place, with the guide it will run in and in the pocket it will stay in. A good, properly done valve job will make or brake the smoothness of the way the engine runs. I believe, many times, the problems with the erratic running can be attributed to leaky valves and cause many other systems to be blamed for this problem when adjusting these systems does not cure the problem.