Honda GN4 is non-synthetic oil. The weight should be 10w30, but depending on where you live, riding conditions, I'd use it for a couple thousand miles, and just change it back out. 10w30 is a slightly thinner oil than 10w40. 30 or 40 being the viscosity of the oil at temperature. Note, these are tiny differences undetectable by the human eye, once the engine is at operating temperature. If you live in a warmer climate say Central US south, and change your oil every few thousand miles. GN 10w40 will work just fine.