Try another spark plug in the trimmer.
Running on a booster gap is usually indicative of a fouled or faulty plug.
I've seen a mower that would crank with the plug wire off, but wouldn't with the wire clipped onto the plug.
Was a slight "what the heck" moment till you realized the spark was jumping from the wire to the spark plug top.
(we're getting into why lightening strikes are so crazy, etc, here)
The problem came from the customer running the mower with the throttle pushed all the way, which engaged the choke and soot fouled the plug.
This was back in the early 80's when you could still see a few manual choke carburetors on push mowers.
I personally will no longer run a resistor type spark, for the reason of having them fail and cause hard starting and missfireing.
No advanced ignition timing or compression changes in any instances.
Fresh non ethanol fuel running in a motor and never lugged
or overloaded, etc.
One motor is 29 yrs old, So I'd guess that I'm not abusing it or the plug.
The plugs just fail.
When you check a bad one with an ohm meter, you'll see a noticeable increase of the through plug resistance.
But that's just my personal adventure, other folks like them and the factories sell a lot of them.
Edit: If this missive is too far off track and overly cluttering Foggys thread,
Then I'd be happy to see a Moderator make it disappear.
