I have an LA 40 that I got when I bought my Avistar RTF. It's to a point right now (well was when it was installed) where it would start in two or three flips cold. I followed the manual settings exactally to start with, from there it was a matter of experimenting with numbers of flips when I primed it, etc etc. It was a bear at first, especially since I didn't have an electric starter, but eventually it came around and became the reliable little monster it is today.

Follow the directions... if you don't have a manual, download it, read it.
18%-20% oil content shouldn't make that much of a difference.
And don't worry about the fuel running back down the line, when you figure out the prime the engine will run long enough for the fuel to flow. Bothered me at first, but not a prob.

Andy