even orginal ngk are crap,,
have problems vith them in my yamaha fs1..thanged to BOSCH w 175 t1..and it run ..on my littel honda i use NIPPON DENSO..
on my 550 i have bad new plugs,,, only have run for minuts..and then it break down..put the old back in ..and it run perfekt...so thange not vorking plugt if they looks fine in isolator..its vaste of money..and give not more safty then the old plugs..i have alvays spare plugs in my tool boks instead..