If you haven't yet removed the heavy oil additive, I would remove the OHV cover and spoon it out before it gets to the oil pump. The oil thickeners usually spell death to an engine by fouling oil pumps, passages and coking the engine beyond belief.
If you have already got the stuff into the sump, I would heat the engine (don't run it, use a heater) and drain the oil and change the filter. Next, run 1/2 Rislone oil treatment (the sweet smelling, blue-green stuff) and 1/2 engine oil with a new filter for about a week or 100 miles making sure the engine gets fully warmed. Drain and refill with the correct oil for your engine this time adding only 1/2 quart of Rislone to the new oil. Also, change the filter. You may find after the Rislone, you engine uses less oil. This is due to the Rislone softening valve stem seals and rings being de-coked. Good luck.
If you have already got the stuff into the sump, I would heat the engine (don't run it, use a heater) and drain the oil and change the filter. Next, run 1/2 Rislone oil treatment (the sweet smelling, blue-green stuff) and 1/2 engine oil with a new filter for about a week or 100 miles making sure the engine gets fully warmed. Drain and refill with the correct oil for your engine this time adding only 1/2 quart of Rislone to the new oil. Also, change the filter. You may find after the Rislone, you engine uses less oil. This is due to the Rislone softening valve stem seals and rings being de-coked. Good luck.