'86 n/a throttle plates not fully opening
 

Hello All,
While still trying to figure out why my engine quits while hot, I found that the throttle plates would not manually open fully.
I disconnected the linkage to the OPM and found that the throttle plates easily open.
My question is two fold:
A. Is it common for omps to seize and..
2. Does this mean that it's a good that I've been pre-mixing for the past 6-8 months.
Any ideas as to a cure to this problem?
TIA, Joe