I have a manual that says to use 20w40 for motor oil. however, a guy at the local parts store who rebuilds old British bikes suggested that there may be something better to run because we have more options for oils and synthetics now than we did in 1975. I am a new owner of this incredible bike and would like to run it at its best. any suggestions or input? also, I have been having issues starting it. like I said, I am new to it. I know they can be particular. I am going through it currently. the gas line is fine, the spark plug is also. I am going to remove and clean out the carb next. but any suggestions are very welcome. I love this motorcycle.