I don't think I will be much help but some thoughts.
Maybe look at the plugs to see if it is really runing to rich.
There is a test called the choke test. You pull the choke half way. If the problem gets better you are too lean, it it gets worse you are to rich.
When starting does it just crank and not start? If so you might want to be sure you have spark. Could be the pick up coils.
Do not give it any gas when starting. The throttle position sensor advances the timing. This would cause the engine to kick back against the starter if this were the case.
Loosen the gas cap and see it it starts easer. To be sure the vent is OK.
Be sure your fuel filter and air filter are OK. They would have to be pretty bad to be the problem but could be.
Maybe some more info might get you more answers?