Problems starting in warm weather?

It starts no prob no matter what temp when the engine is cold. However, with the warm weather we've been having in MA its "warm weather problems" came back. It put up a good fight today when i tried to start it after the engine was warm (outside temp was about 55). Usually when i have trouble starting it like this, the exhaust will smoke a little upon startup and i'll have to pump the gas quickly as it slowly chugs to life. Could this be due to a lack of back pressure from the aftermarket exhaust? I was actually told its done this its whole life, but theres got to be something to do about it.

Check the choke adjustment. The blade could be closing too far for warm temps, or your choke pull-off is not working.