Hi Terry , ok my 2 cents
If your sure its not a fuel problem , and you have replaced the plug
try and borrow a grey coil from some one , chances are its dead , just because you have spark on the plug when its out of the engine it doesnt mean it will have spark inside the combustion chamber , its a very different environment in there
and grey coils are notorious for being the weak link . some times they last years other times days ...
you may want to also check the air gap between the red coil and the flywheel , stuff a buisness card between it to get your gap , tighten the screws and remove the card , it will get you remarkably close to what you need
I also use NGK plugs not Champions
and although other people have had problems , i have never disconnected nor drained fuel nor run the fuel from the engine , and have stored it with line connected for up to 3 months - then primed the engine ( trying to start engine with finger in carb till it fires once )
then the engines runs next pull
I run them at 30:1 using Motul 600 TT synthetic oil , engines run clean and never had a problem, 25: 1 is certainly not a problem either - your lawn mower has been running fine on that mix for years :lol:
Zenoahs are pretty **** tough , seen them run without water for an entire race and survive , if they dont start easily in my experience its cause something ( plug or a coil ) has died
I hope that helps
Andrew