Put 30W Low Ash engine oil in it and see how it acts before tearing it down.
Ok, so here will come all of the haters of proper oil grades...... "my neighbor's barber's uncle used kerosene in the crankcase for years..."
I should have made a video of the poor old 140 That I just put through the shop 2 weeks ago. The oil was thin and it would actually pool on the pistons. I put 30W in it and it changed instantly. It is off to run the Woods Mower again with a happy customer.