Honda Harmony 2013

I am still using my Honda Harmony 2013 and I just replaced my cutting blade belt. My problem is, the PTO arm will not stay lock or it disengages in any height level when I turn it on. I followed the instructions from the maual to a T and its just not working. Can somebody out there be kind enough to let me know what I did wrong or tell me how to correct the problem. The belt I use is a honda P/N and it is 88". I checked all that is needed to be checked and it still will not stay lock or does not stay in the on position when I push the PTO arm forward. I would appreciate any helpI could get from anyone. Thank you