I thought it was just my HRX217 lawnmower that oscillates wildly during
idle. But then I rented a Wacker trash pump with a honda engine, and it
would also oscillate when in the full throttle position whenever it lost
prime. Then I rented a pressure washer with an 11HP honda engine and this
too would oscillate heavily at idle when the water was not being sprayed.

The fluctuation is pretty severe, as if the engine is going to stop, it
doesn't sound normal at all. Since it happened on 3 engines in a row - I'm
starting to think it could be the gas I'm using. My gas cans have a mix of
89 and 91 octane from Mobile. Could it be that the octane is too high? Am
I supposed to use 87 octane instead?