In my old vehicles, '71 Chevy Van, 250 c.i. in-line 6 and my '56 Allis Chalmers farm tractor 4-banger engine, I use Marvel Mystery Oil. It comes in 1 gallon plastic jugs now. Follow the instructions on the jug. It's about 2 ounces of MMO per 5 gallons of gas. In the van, I have an old used plastic bottle that formerly had chalk line chalk in it. I used a magic marker to mark lines on the bottle so the bottle has exactly 1/3 bottle marks. When filling up, I simply pop off the cap and pour in 1/3 bottle of MMO then pump the gas. MMO works like lead used to without the air pollution qualities of leaded gas. It acts as an upper cylinder lubricant and acts as a "cushion" for the valves like leaded gas used to do. Van has 115,000 miles on a rebuilt engine. No valve issues. Tractor is a '56 so I have no idea how many hours are on it. No valve issues. As I get my gas for the tractor via a 16 gallon steel drum that I fill up at the gas station, I place the appropriate 6 ounces of MMO into the steel drum at home prior to going to the gas stop. I use this gas out of the drum for my log splitter engine, chain saw and weed whacker, also. Log splitter is a 4-stroke. The two-stroke engine gas is mixed with the appropriate type and amount of 2-stroke engine oil in a separate small container. Works for me! No valve issues on any of this stuff.