I am seeing the spec to be 133amp at stall
http://files.andymark.com/CIM-motor-curve.pdf
As for breakers
http://www.snapaction.net/pdf/MX5%20Spec%20Sheet.pdf
Based on that spec sheet at about 120amperes a 40 amp would trip in .5-1.1 (300% load)
Their graph is flawed I believe, if you count there are 11 graduations starting at any number x and going to 10x including x's and 10x's, conventional logarithmic scale should be 10, eg 1 2 3 4 5 6 7 8 9 10. Additionally the data seems to be a little different than what they say in text.
Maybe provide some more information so people more experienced than I can help figure out your issues.
What is your:
Wheel Diameter?
Gear Reduction?
Coef-of Friction (if the calc has it)?
# of CIM's in Drivetrain.