Greg Copeland writes:

On a large rotory engine, only 1% methane contamination was
required to cause the engine to quit. Less than 1% was enough
to cause an RPM drop. As it approaches 1%, sputtering occurs and then
finally, the engine quiets.

I'm not sure that I caught everything correctly when that was happening
but I thought someone said that the methane caused an over-rich mixture.
So...what happens if you lean the mixture?

--kyler