Castrol 0w-30 German, for cold weather (0-50F) in Honda Eu series generators.I had Castrol "made in Germany" PAO 0w-30 in my Honda Generator up in Montana on Sept 11, 2014, and the temps were down to 17F in the morning when my Eu2000i started right up, first pull. Steam was coming out the pipes for exhaust that morning, whole time the motor was charging my battery.
If you know you'll be in real cold, switch to a true full synthetic 0w-30 for that trip, if it's important to you.
I almost always start it up on ecothrottle, and let it warm up 2,3 ,4 minutes before putting the motor under load.
Cold engine parts need time to warm up gently, expand, and take up the tolerances in the motor that the cold temps exacerbate, due to differences in expansion rates... aluminum shrinks more than steel in cold temps. Your piston is aluminum, your bore in an Eu2000i, is steel, so take it easy on the motor, let it warm up, since it's air cooled, before working it hard.