GoPiGo2 pulls to the left

Just starting out here. It keeps pulling to the left. I saw an earlier thread but I don’t have replacement motors. I have messed with the wheels and they don’t seem to be rubbing. It pulls on the rug and the hardwood floors. Wasn’t as bad 2 days ago…pulled it out again today and it is worse.

For the pulling one direction or the other, I went through this procedure to “trim the motors” and got mine to go fairly much in a straight line.

http://www.dexterindustries.com/GoPiGo/programming/python-programming-for-the-raspberry-pi-gopigo/add-trim-to-the-motors/

Hope this helps.