Lately a friend has been having lots of top end engine problems and I cant seem to figure out why. His stock zenoh 26 on mb was running fine suddenly it locked up we removed plug , was clean maybe slightly lean but far from extreme top of piston showed no signs of detonation little bit of carbon starting to build up, but ring stuck . After asking around we determined that our 32:1 mixture maybe the issue so we went to 25:1 . We pulled head on his stadium truck to change head and piston to 28.5 specs and use top end on mb. After removing head we noticed that this ring was on its way out, looking at this plug its clean ( no white or tan coloration no black carbon buildup) we replaced the 2nd head with reed ported head ,thinking that its still the same fuel problem. Both of these engines have only had approx 3-4 tanks run thru. After break in he ran engine hard and behold another seized piston ring after pulling this plug this plug shows sign of being rich(slightly oily black carbon ) anyone else having this type problems? The really weird thing is during this time I've been running my race runner and rally car with no problems using fuel from same can I don't run as hard or as long but this appears unusual.