pop the advance cover off, see if there is any change to the gauge by playing with the advance piston or cold start..does the cold start lever change the reading of the gauge when you pull it out?
Sounds like a winner to me. Great to have extra parts on hand. I am in the process of rebuilding a pump myself and besides a bit of pitting here and there I think getting all the varnish like gunk off and letting the little pieces of metal in the rotary pump part actually slide out and meet the walls like they should will be enough to make this a good spare pump. I just need to be sure to fill and seal it well before packing away.
...BTW your Bieber avatar is awesome.-Malone
Might be the injectors. Fresh ones may run right at the normal advance.