try dumping the oil , use 1/2 container of no smoke from the auto supply store then top off with nondetergent 30w oil, which you should be using anyway,

Actually, a detergent oil is better for an engine application. The non detergents are used in pressure washer pumps and air compressors where there is no blow by. The detergents will eat up o-rings.
Rings only are like putting a band aid on a chest wound. You likely have a K241, great engine but tired after 27 seasons. A complete rebuild is likely in order.

" then top off with nondetergent 30w oil, which you should be using anyway,"

NO.

Walt Conner

Well, I would start off with compression check, then an leak down test, and remove the head and look at the bore and slap between the piston. Outside chance if the bore and piston is good could be a valve seal problem. But, as said above most likely it worn out from lack of oil changes and then not checking the oil level.

Blue smoke during start up/warm up, or when "cracking open" the throttle suddenly is a good indication of worn intake valve oil seals.
Reason is due to the fact that the INTAKE valve stem is exposed to engine vacuum during the intake stroke portion of the 4-stroke cycle, which helps the oil migrate past the worn seal and into the intake plenum of the head where it mixes into the induction draft and right on into the combustion chamber.
Engine intake vacuum is highest when the engine is idling or at very slow RPM because the cylinders are sucking against a closed (or nearly closed) throttle plate in the carb. This high vacuum draws a greater amount of oil past the valve stem seal......but the oil is not immediately swept away to the combustion chamber BECAUSE.....there is not very much air flowing through the intake plenum with a closed throttle........just the bare minimum that it takes to idle the engine.
Then, when you crack open the throttle to increase the RPM, the inrush of air through the now open throttle plate sweeps the oil "puddle" into the combustion chamber.