As for dealers not being willing to do warranty repairs on units they didn't sell, it's in part because warranty repairs tend to be losing propositions. Manufacturers will only reimburse for flat rate plus parts and their flat rate schedules are established with expert technicians working in perfect conditions. It's not easy to match flat rate times in a working shop. It's one thing to lose money on a warranty repair for a customer who purchased from you and whom you would like to keep, it's another to do one for a walk-in who may never give you another dime.

Not saying it's right, just saying that's how it is. I've worked as a dealership mechanic.

BTW, while I presume this is a new motor and designed for today's lower octane gas, the same doesn't go for older motors. Some won't run at all on regular, other may run but will run much better on mid-grade or premium.

I've had the experience of buying gas that my car will run on but my old small engines won't.