Mine did the same, when new. I needed to change to a new brand of plug, (not Chinese). Finally when it sputtered, I pulled back the clutch to get it to rev it like in neutral to get it to warm up. Mine wouldn't hardly run on 16:1 so I changed to 24:1 after a tank full and it runs much better and starts much easier. I want to go to about 30:1 eventually.