As a first guess I wonder if you remembered to oil the crankpin when you assembled the big end? Anyway, all's well that ends well. Tuning the carburetor should be easy when the governor is working properly, just follow the Briggs instructions quoted in my post earlier in this thread. At this point I do not know whether you have a mechanical governor or an air vane governor, but my first guess is that it is a mechanical type, like this:
[Linked Image]

You can read the details on it here:
http://www.tpub.com/content/recoveryvehicles/TM-5-4240-501-14P/css/TM-5-4240-501-14P_148.htm

I expect your 28000 engine will be similar to a 25000 engine - the 28000 is not specifically covered by the manual.