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Author Topic: M91 water cooled vertical H&M. A recap.  (Read 291 times)


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Re: M91 water cooled vertical H&M. A recap.
« on: May 23, 2021, 06:32:25 pm »
Very interesting & helpful info gentlemen!! Todd over on "Project Farm" has a good, exhaustive non-leaded pump gas to Tru-Fuel comparison test results, proving surprisingly, that Plain 91 Pump Gas produces a Longer Small engine Run time with Less piston & valve Deposits !! ...I've only used straight Coleman stove fuel in my Stock (weaker govenor springs mod) No head or piston mods M-91 engine...Your postings has me rethinking  gas fuel "Reid" Vapor Pressure spec. (Volatility) differences between the various mentioned fuels..My M-91 runs so Cold it never really  gets up to an optimal Carburator running temperature...I'm sure the pure, Non-Lube added Coleman fuel burns Cleaner than Any Gasoline fuel product & my non-loaded running shows No octane Knock issues..Regarding fuel Volatility, the significantly Lower (5.0) vapor pressure Coleman compared to Gasoline's 8.5 psi Vapor pressure could Possibly be Improved by adding Highly Volatility Butane to a tank full to help better Cold carb Vaporization ??...After > 1.5 yr running, still runs like new & Easy 1st flip Hand starts on original sparkplug....Ideas ??.......tom.


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