There are 2 'myths' associated with leaded fuel. 1. Leaded fuel will let your bike make more horsepower.
2. Leaded fuel protects your valve seating surfaces. First: lead as a gas additive will raise the octane of an existing mix, but unless your bike is pinging on the gas you are using, more octane doesn't make more power. Second: Engines that were manufactured with valve seats made out of soft materials like a 1964 Harley Davidson or Triumph would slowly have their valve seats eaten away by unleaded fuel. But even the 1969 Honda
CB750 had valve seats made out of Stellite or an equivalent hard material that can tolerate unleaded gas (there are still a zillion of them running). Modern bikes were designed to run on unleaded fuel by smart engineers who are not going to put cheap materials in the wrong places, I mean they've got titanium valves!! It's probably going to take another 20 years for that myth to die. Lead was banned by the government over health concerns from both gasoline and paint.