My friend (Kevin) has just acquired a Honda 3011 riding lawnmower. The owner drove it up onto the trailer but Kevin can not figure out how to get it started. We are certain that it must be some sort of interlock. Please advise.

you haft to set the parking brake

http://www.hondapowerequipment.com/pdf/manuals/31763800.pdf

see if this will work.

you haft to set the parking brake

I think this is enough .....
I do agree with you. Those are the most effective way:(

UPDATE:

Come to find out he was not engaging the choke. He was pushing the lever as far as "slow" and thinking that it was choked. Thanks for the responses and the pics.