I'm having this problem also and I have checked all the above and it just don't keep running.
As soon as I stop pedaling, it'll come to a stop very quickly.
My initial guess is that I made a mistake pouring in the oil first before the fuel, and not mixing it enough. Thought I'd pour in the oil, pump up the rear tire at the petrol station, fuel it up while I'm there, and shake it up.
Well, as soon as I opened the fuel valve, the oil came straight down; no mix.
Well, engine didn't start so I had to bleed out all the oil until it was mainly fuel coming out with slight oil mix; still the same problem. It starts a bit better, but still dies.
My next guess is maybe the CDI? This is a 1.4KW engine, and when the CDI arrived, the cap which connects to the spark plug was broken, so I'm using a previous CDI I had for a 200W engine; maybe not enough power going through?
I've just read this thread:
http://motorbicycling.com/f34/struggling-make-bike-run-25270.html
I'm hoping there's nothing broken...
Any help?