Make an air gap tester, the cost is probably $0, you have everything you need already. Here is what I did. Racerone does it even cheaper, he simply glued some wires to a piece of cardboard.
I can bend the wires to any gap desired...every 2 stroke I’ve tried, (weed eaters, chainsaw, kicker) will drive a crackling blue lightning bolt across almost 1/2” gap. If it won’t, you need to look at ignition.
I used a couple pieces of 14/2 household wire. Wrap it around the screws, & turn them down so the wires won’t move closer. I stained the wood dark, easier to see the spark in bright sun.
The 1/4” bolt makes it easy to turn into the spark plug bolt & make a good connection. Just put the other end in the empty spark plug hole in the head. The weight of the tool & angle will hold it securely against the head.
