2012 Merc 200 Pro XS Spark Plug Fouling

[bassman3800]

Spark Plugs were replaced at 100 hours and at 200 hours and now at 230 hours the #5 plug fouled out completely. It was replaced. Two trips later all the other plugs fouled out. Dealer says computer check shows no issues and coils all checked good. Last time out max speed was 8 mph so I limped in. I run no ethanol gas and add 1 oz per 10 gal of fuel stabilizer and 1 oz per 10 gal of Yamaha Ring Free at every fill up which is usually about 35 gal every 3 months. I have to idle thru no wake zones and idle when looking for fish but usually idle time is no more then 15 minutes at a time. The first indications of problems I notice are "no hole shot" and occasional skipping. Any suggestions???

[06 SB]

This should be in the 3.0L section. Also, please post a serial number as that will allow the experts to get you better advice. There were some significant changes in the 200 ProXS at that time.

[bassman3800]

OK thanks I moved it to that section.