Greetings Mr. Bond,
How did the fuel system parts look that you serviced/replaced? Were they dried out, coated in varnish, etc?
It doesn't sound like an ignition problem, but if you are even considering replacing the spark plugs, just replace them. I am partial to platinum plugs.
The next thing I would look at is the carburetor. Take it off, take it apart, and make sure that it is squeaky clean inside. Blow out all of the passages, and use a torch tip cleaner on any that appear blocked. And replace anything that appears broken or worn.
Have you performed a compression test on the engine?
I know, more questions than answers, but need to know the whole story.
Cheers - SR