Put in a new spark plug and make sure your air filter is clean for starters.
During a hot, humid summer day, there is less oxygen in the air than on a cool dry winter day. If your bike runs good in winter, it might be a too rich for your current weather conditions.
You can lean it out a little by turning out the airscrew, and by moving up the needle clip 1 position (putting the clip in a higher groove will drop the needle further into the needle jet). No $ required and only takes a few minutes to do. If it makes an improvement but not enough, you will know you are on the right track.
Check your manual for the location of the airscrew and the needle clip.