About three weeks ago I took my newer Moki 215 to the field and had great trouble starting the engine. It would start then lean out and die at low warmup rpms. It dawned on me that I might have a sticking valve which will allow the crankcase to suck in air through the exhaust. Sure enough I had three gooped up exhaust valves. You can tell by manually with your fingers press a valve and it will be harder to depress and it will return to closed slowly. I took the engine home and used brake cleaner to free up the valves. Spray into the valve stem...wait for the cleaner to dissolve the carbon/oil crud and spray again. I did more runs at home and the valves started to stick again. I have been using Amsoil interceptor oil on my older Moki with no problems. I have some Redline two stroke oil which DA uses so I mixed up a 44 to 1 batch with Phillips 66 premium. Since then I have flown at the field three times. Last Wednesday was a 3 mile/hour wind day and I flew 9 times. The valves are as free as a bird. This is hardly a scientific controlled test. Redline does leave a bit more residue on the plane than the Amsoil suggesting better lubrication. Maybe the newer engine has a tighter fit of the stems to the guides....who knows? Anyway I am pleased with the results. -Tom