I strongly recommend Catrol oil. I have noticed it helps my bike to run smoother, and also has given my old beatup Geo Prizm a few more mpg intown driving!! It's pretty good stuff
I'd suggest synthetic oil, but wait until you get up to above 10K on mileage. A brand new engine needs time to get broken in. All the metal parts get fitted tightly at factory and an engine just needs time to "find itself'. Kinda like breaking in a new pair of shoes. Once that's done, then go ahead with synthetic. I use it and it's also given me an extra 1-2 mpg. But it helps best with lubrication, because it's much easier on engine to run it. Yeah, it's lot more costly, but it'll keep engine working smoother for so much longer.
Just keep changing oil constantly so you've got good clean oil, and you'll have that engine for decades!! Running old oil in car engine will ruin it the easiest and hardest.
