Re: used sparkplug in new(?) engine
What Pablo said...and I'd also look for signs that the engine had been mounted before. Check the mounting areas and the bolts/nuts for evidence that a wrench had been applied. I recall reading here somewhere where a member had received an obviously used engine and his seller wouldn't do anything about it. Who did you buy the kit from and have you contacted them? Good luck, keep us posted, please.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"