Yamaha 150HPDI VZTLRZ Fouling Plugs

[skeeter4848]

The engine is a 2001 fuel injected. The problem is a plug or plugs are fouling. I have put in 2 sets of NGK BKR7EKU (5881) plugs within 2 months. With the new plugs the engine runs strong. The plug is a dual element plug. The gas is non ethanol with staybilt and seafoam added on a regular basis. When I remove the plugs I cannot determine which plug or plugs are not firing. The plug tips are black but none of the plugs appear to be "wet". I tested one set of plugs using my lawn mower as the voltage source. All 6 plugs fired; however, that does not determine that the plugs will fire under compression. In 2010, the engine was service by a Yamaha dealer: new electric fuel pump, new in line high pressure filter and new gas lines. I have visually inspected all 6 cylindars. There is a light coat of carbon on the top of the pistons but no other apparent problems. When I am running at 3500rpm's, the tac has started to jump up to 5000rpm's with no change in the engine performance and then return to 3500rpm's. I am going to attempt to clean a set of plugs and try them. Could this a coil going bad or getting weak? Will the computer give a mechanic the codes to fix the engine? I do not want to start just replacing parts. That gets expensive.
HELP! Any suggestions will be greatly appreciated. Thank you. emoBang