When I ran 1340 cu. in. Pratt @ Whitney engines, they'd sometimes suffer a stuck valve and we'd attach a plastic line to the intake and feed MMO while the engine was running and smoke the whole airport with clouds of blue More often than not, the valves would unstick and we'd be on our merry way, so I became a believer in MMO for THAT purpose, because it worked.
Last year, I squirted MMO in a Honda lawn mower's cylinder that had sat idle for 5 years and left it overnight because the engine was "frozen" and let the MMO penetrate the rings and lands. Yep, two days later, it freed up and actually ran! The carb had to be disassembled and ungunked but we're using the lawn mower and my wife loves its easy starting.
It (MMO) has a place and I keep a can of it around but don't use it in any of my airplane engines.
The previous owner of my engine added a qt at every oil change for 700 hours. I'm not a fan of the stuff but many are. There was a trash truck company around here that bought it in 55 gal drums I've been told and swore by it in every truck they owned. I think it's mystery includes pig fat and perfume. I'm not using it now and I hope the engine doesn't miss it.
More often than not, the valves would unstick and we'd be on our merry way, so I became a believer in MMO for THAT purpose, because it worked.
