Opened up the valve cover and found valves were stuck. Hard carbon found on surface of valves causing lock-up. One valve had more carbon buildup than the other. Cleaned and started the edger after maintenance. Now blue smoke comes out the muffler, plenty of power--otherwise works fine. Question: What's causing it to smoke? Anyone--think it needs NEW RINGS and/or NEW VALVES? Also very slow oil leak at rear oil drain plug. -Javier