Hi All, Two questions: -What spark plugs should I run in a TIO-540 with 7.3:1 compression pistons and a dual LSE Plasma III ignition systems. -How can a spark plug go bad after only 10 hours??? I just had a NEW NGK BR9ECM spark plug go out after about TEN HOURS... So what can make a spark plug go bad??? All of the spark plugs that came with the LSE kit are Denso W27EMR-C plugs and they have about 200 hours on them and they were working fine. When doing an inspection I dropped the one plug and cracked the ceramic and since the original plugs are no longer available I cross referenced to the NGK and put it in...ops check good and flew for about ten hours. Then it up and quit. To make the trouble shooting difficult I had pulled the engine out and replaced the oil pan and did some ignition wire rerouting and some other work to the airplane and then when it came time to fly the engine ran rough...lots of troubleshooting and head scratching and after the long ordeal I swapped spark plugs from #3 to #1 and the trouble followed As you read from my other post...the ignition system was running rough and naturally I pulled and inspected the spark plugs and there was no damage and no cracks...a bit black due to rich mixture...the idle mixture was set at sea level and I am now at 2200 MSL so I simply lean during taxi. SO what would cause a spark plug to go bad without any physical indication that it is bad??? Again...the only way I found the problem was to swap the plug from #3 to #1 and the problem followed so it must be the spark plug........................ THANKS for your help!!