I have a Northstar generator with a Honda GX620 20 H.P. It has around 100 hours on it. I used Napa universal fleet 15-40 in it for the first two oil changes. It calls for 10-30 or 30W. I see now Honda has a synthetic oil for their power equipment. I am now thinking of using a 10-40 synthetic maybe like Shell Rotella or M1 15-40 Delvac. These oils are higher in zinc than car oils and this is a flat tappet engine and works hard here in South Florida. It had done fine on the Napa but requires 50 hour oil changes. I'm thinking I can go to 75 with a good syn. Thoughts anyone?