before you spend hundreds of $ replacing perfectly good parts, go out & buy a Gunsons Color Tune.
I use mine a lot, in fact I now have 3 of them.
Replacement spark plug with a window in it.
Start the engine and watch what happens, what colour the flame goes and weather there is a spark happening after the engine starts to shut down.
Excellent piece of kit, around $ 30.00
Gunson | Tuning
It wil save you hundreds of hours and thousands of dollars.
Only 2 problems
1) dont put you gob one the top of it and give the engine full revs ( should not be a problem on a mower engine )
2) don't get facinated by it and watch it for hours on end
