I have a Generac 16 KW Generac Natural Gas standby unit 3 ½ years old Model 0064592. Serial #50065139
It failed to start for weekly exercise and showed error code 1100 (overcrank)
Stepper motor leads ohms are (red common) Orange 11.6, Yellow 11.6, Brown 11.7 and Black 11.6
Throttle Plates do not open when cranking (manual start button)
I can open top throttle plate about ¼” then external linkage stops it because bottom throttle plate will not move
Last service date 5/18/18
Natural gas feed 15 feet 1 ¼ pipe
Evolution control
shade tree- I had a similar problem on a 16KW also. Stepper motor (governor) ohmed out OK. Ended up changing controller since that's where the signal comes from to operate the stepper motor. After changing the controller, the stepper motor operated correctly.
If you can't move the lower throttle shaft, you need a new stepper motor which on an evolution unit is the entire mixer assembly.

It is conceivable that something is in the venturi pipe, or that a throttle butterfly has come loose and is jamming, and that may could be fixed.  Which would require removing the mixer to investigate. You may as well, and either repair it or install a new mixer.  

But I most definitely have seen frozen stepper motors.

The lower throttle shaft, the one attached to the stepper should move through its full range with some drag caused by the gear reduction.
State your problem, not your diagnosis.

I had issue with mine with a high resistance connection to the stepper motor cable connector. Just un-plugging and re-plugging a few times fixed the issue.

Like MacL noted the shaft should feely move. Possible a backfire bent the shaft.

Thanks for your support. I ordered a new 
stepper (entire Mixer assembly on this unit) and Installed it today, all is good, (generator starts up as it should!