keep at the flooded engine procedure. you may need to go through a few battery charges, but if you're not interested in that sort of thing, use an automotive battery.
just hold it wide open all the while cranking. do not back it off, do not snap it to zero... it will not start EVER with the throttle at 100% during start up. zero fuel is delivered while cranking like this. you will never ever ever get it to start with the throttle at 100%. never. when you attempt to start it normally, take your hand OFF the throttle. do not touch it. when it starts, let it idle. for a while. until it gets up to operating temperature. then go for a ride. a short one. make it brisk, but legal.