Premium unleaded and additives are a waste of time and money in a lawnmower, the only reason I would put 98 in one is if I couldnt get my hands on non ethanol fuel. I drove a holden 202 on straight ULP for close to 10 years and when the head was removed, the wear was marginal on the valve seats but not that bad, especially considering I was doing on average 500km a week.
