1995 Yamaha 85 fouling plugs

[Marlinman10]

After about 25 hours on a set a plugs they will foul while trolling. I fish off shore here and do a lot of trolling at 1800 Rpm. should this engine be able to troll all day without this happening? I just got it back from the shop and they said it checks out other than doing a de-carb. I'll have it out this weekend and try again. I use Yamalube at 50-1 mix. Also it only turns 4000 rpm at WOT with a 17 in pitch prop. This seems low. It's on a 17 foot Glasspar that weighs 1100 pounds. I need a expert opinion. Thank You

 

[robert graham]

Re: 1995 Yamaha 85 fouling plugs

the correct prop should allow for a WOT of 4500RPM to 5500RPM...could be the prop is the problem, but was it running better/different before this plug fowling started? is your thermostat allowing engine to get to normal operating temperature? if not, it could give you that rich mixture and fowled plugs. I run a 90C premix motor and can idle all day at any RPM without fowling plugs. I do run the Pennzoil Marine 100% Synthetic oil(Walmart $27/gallon) and it runs very clean with little smoke. if your motor was running good before in the 4500 to 5500RPM range then maybe an engine temperature issue. Hope this is helpful and Good Luck!