I can tell anyone, first hand that ZDZ engines need proper tightening of the spark plug. After purchasing a new in box ZDZ 80 and a new ZDZ 80, I tried to tighten the plug with the supplied wrench and it SEEMED tight (both came with the spark plug installed). Then, after a few flights the plug came out in flight on the new engine! I know it was my fault for not checking the plug tightness but, after using the proper tool it has never happened again. The two MVVS engines that I own did not come with the plug installed so, I used a larger wrench to tighten them, as a result of the ZDZ experience, to a nice snug fit before even the first run. I have not had ANY problems with the two MVVS 160's that I run, after two gallons thru each.

BTW I agree with andyt, completely, .....Now.
Jamie