The area just above the threads on the supplied Chinese plug is a lot smaller than the i/d of the washer.
This washer can go off center and cause a sneaky leak that causes oil to blow out and some misfiring.
The only way I was able to find it was to remove the plug cap and put some alcohol around the plug then roll the engine by hand and saw a lot of bubbles from the leak.
In addition....my plug had egg shaped threads...I asked for a warrantee replacement but was denied...so I tossed it into the weeds next to some of Rene's Rossi carbs and got me some Rimfire plugs that are great quality.

Also...I had a huge problem that turned out to be a bad joint where the hall effect wire was connected to the backplate.
I could fly around and do a positive pull and it was ok....then do a negative push and the engine quit just like a rag was tossed in the prop.
I finally found it by running it on the test stand and moving the wire by hand.

There were so many quality control and design problems that I lost a year and a half of flying in spite of some of the most experienced help in the world both locally and on the phone.
Finally....I left the damn thing where it quit last...plane and all....done.
I've been flying something else now for 2 1/2 years with no maintainance.....I never thought I would get to that point but I did.