Have a D170 with 69 hrs on it. Yesterday while mowing grass engine suddenly got a bit louder and now has about 70% of the power it had before. Put gas in it checked the oil ( fine still clear and no smell of gas in it). Let it sit, today I checked the plugs 9 see pic) and gapped and changed them and still have the same issue. Any ideas? BTW this is the B&S 25 Hp engine.