I've got the same problem, I can do them of the smallest of speed bumps but when I try it flat, I barely get it with one foot. I've been trying to focus on the bars staying right in front of me and keeping my eyes on the deck.
I broke two trampolines doing it, haha. My parents told me not use my tramp scooter any more cause they didn't want to buy anymore trampolines, it was fun while it lasted though