Small Engines (Lawn Mowers, etc.): mowers wont run, stroke engine, fridgidaire

Question
Unit 1: Fridgidaire Homeproducts, Mod Q375N22SA Ser 030800M004285.  Used this mower most of the summer, ran great, it recently lost power and doesnt want to run for long.  Plug is fouled,  oil is very black - even after changing both, same problems persist.  No power, stalls under a load.  Is this worth fixing?  If so how?

2nd Unit:  Homelite, Model UT30119A, ser JK0820263.

Two stroke engine ran great last time I used it.  Gas was drained for storage.  This season it wont start.  It will turn over with starting fluid sprayed into the carb, but just wont run.  What gives?

Answer
I would pull a compression test on the mower. I would expect it to be lower due to either a burnt exhaust valve, or bad rings.......The trimmer is in need of a carb rebuild, I would also remove the muffler and check the spark arrest screen on the back of it, making sure it is clean, and not blocked with carbon.........Tom