after cleaning the engine, try a novarossi/rb plugs. They are better qlty. Sometime you do get a bad batch of plugs. Are all 4 plugs from the same sheet?
I use only Nova/RB plugs on my Nova/RB engine. try a 6.
rich up the top and botm a little and use a heat gun to heat up the engine.
If that does not work, then the engine is probably shot.
Also make sure the piston is installed correctly. I got an used engine before, the guy put the piston in backwards. The engine would start and die.
The oil hole on the conn rod is toward the front of the engine, the piston (if it has a cut is toward front of the engine) PLS Correct me if I am wrong.