Prolly best to use synthetic, I have older machines and use Amsoil, there are several out there. Without the OEM oil pump you will use more spark plugs cause of idle fouling but think of all the bugs you kill near the shoreline - this debate will live on forever. The ratio I have read the most is 40-1, and in the begining of the season I use this and the oil pump, just to make sure the motor is drinking oil like normal - on some motors you still have to check/drain/refill the counterbalance shaft oil so eliminating the OEM oil pump does not mean less maintenance, observe the technical manual for your motor to be sure about the oil port.