Lot more soot build up around the prop, bit more smoke that had bad smell at idle, and plugs tops of pistons carbened up

 That being the case did a clean up with the evinrude aerosol carb /inlet cleaner spray.. do it on the water calm day if not have a unit that loads the prop to take rpms up free wheeling.

 As that the 115 was min powered on the 5.5m  boat  stepped up to the XD 50.. 

 Far cleaner than both the XD30 and dirty valvoline.

Now run a 2001 150hp johnny  still run the XD50

If changing oils, do not mix them, types and brands.. even the XD30 and the valvoline.

  Clamp off or disconnect the oil line at the tank put a screw up inside to stop draining.

Tip out remaining oil.

 Check no water  debris to screw up the sensor in the future.

Pour in new oil

Reconnect oil line to tank.. dont let oil inside drain back.

pump up bulb well.

Instead of assuming the oil pump is primed , no air locks, I fire up and run the engine on a a couple Litres of pre mix  50:1 fuel.

2x oil mix will smoke a lot.. If mark the tank with a dine line you will see marginal drop in level.

Suggest while tank is MT.. and re filling it, as you put each L of oil in , mark the cnr of the tank with a sharp bait knife each L... maybe smaller mark for 500ml icrements

 Yes brand oil is expensive.. I shop around agents and buy 20L drum.

 Keep in mind , no lube or bad lube so death to the engine.

Carbon up , higher compression, throw timing etc off, loss power less economy.. and timing out on these finely tuned engines means slow death also.