I know that there is a trick to starting this engine, but no matter what I try I can not get it started. I have replaced the plugs and checked to see if fuel was getting to the cylinders and all seems fine. Fuel is going to all the cylinders and there is a very strong spark. Yet, she will not start. I have tried to start in neutral with choke, neutral w/o choke, full throttle w/ choke and without - still to no avail. Any suggestions?