checking spark plug ,ends up sooty

[piperdog]

hello,ive a 25 hp ,blueband ,serial no. 5827237 and at the moment its got ngk br7hs spark plugs it and they are sooty on appearance when taken out ,can any one tell us is it because its running too lean and where is the adjustment and are they the correct pliugs ,thanks piperdog

 

[Laddies]

Re: checking spark plug ,ends up sooty

The idle mixture may need to be adjusted or the thermostat may have failed