Waaaay back in 1969 at the Philly nats....I traded an OSMax 35 for a .35 MVVS a very similar one that was used in Surotkin's (spellingsic) mono wheel stunter that used only an outter wing skid...and a tail wheel. I flew it for a while in my old StingRay.
This engine was not brand new and had been restricted quite drastically for stunt. Perhaps this is why it ran very steady...EZ to start...seem to run forever on a 4 ounce tank. However after changing to a larger intake restrictor..and a different needle valve. This old smoooothie turned into a cranky-nasty little engine...that would REALLY UNLOAD AND SPEED UP in multi-loops. But after going back to the original restrictor and needle valve.....It calmed down and acted like a stunt engine again.
Bottom line: I finally gave it away to one of my engine collector nutski's. for a bottle of Ripple wine. (that is another sad story)
APPLES AND ORANGES..ARE NEVER CREATED EQUAL..AND NEITHER ARE STUNT ENGINES.
That MVVS weighed a tad more than the OS 35 but didn't have as much usual power...and wasn't as easy starting as the OS.
With that in mind.....Perhaps that
RIPPLE WINE trade might have not been so bad after all..especially when someone realllly special helped me drink that wine later that night.

This isn't the engine...but it looked very very much like this one???