Poulan pro 4218 bought a cylinder piston kit on eBay

[Tiger Small Engine]

have the correct schrader valve in tester

Then you have really low compression. Can you post your results after rebuild so we can hear how it came out please?

 

[StarTech]

Then you definitely have a compression problem as it takes at least 100 psi for a two cycle to fire the fuel mix.

You may simply have to replace the PNC again or called it too expensive to repair.