You didn't mention if you're using fresh gas and what mix you are using. If you have old gas in there then that will likely be at least a part of the problem in starting up.
You said you have spark so let's assume that is fine for the moment. Did you re-torque the head and did that fix the gap? If that's fixed then re-gap the plug down to 022 and try to re-start. Try with the choke on and off and somewhere in the middle. Choke on is lever up.
Like Greg said, try a better spark plug.
And yes, you may have to peddle a while to get it to fire up. Let's say around ten miles per hour