I suspect I might have a cheap aftermarket piston. Where can I purchase a genuine one? Are there some trusted sources of better quality parts? Regarding the teflon buttons, they would have two diameters. The small diameter would press into the hole in the wrist pin. The larger would be slightly smaller than the wrist pin OD. The head would be rounded. The overall length of the wrist pins and two button heads would trap the wrist pin in the piston. My only concern is temperature.

Chances are, your mower has a type of governor on the throttle mechanism. Hidden beneath a metal guard, there is a small vane, that sits in the airstream of the fan, mounted directly on the engine crankshaft. If the engine speeds up too far, the vane pulls the throttle closed, in order to slow it down. There is a small spring, usually visible, that pulls the throttle open. So, the vane and the spring work against each other. When the engine is not turning, there is no airstream from the fan, and the throttle is wide open. When you prime the engine, using the rubber primer bulb, you put some extra gas into the carburetor. The engine will start and run rich, for a few seconds, until the slug of primer gas is burned up. Now, the engine has to keep running, with gasoline delivered by the carburetor. If the carburetor is clean, and free of gum or varnish, the engine will run smoothly. If the carburetor is gummed up with varnish, deposited over time, the engine will run lean, start to stall out, which causes the spring on the throttle arm to pull the throttle open. Now the engine zooms, but not for long. It starts to stall again, and the cycle repeats. Until you clean the carburetor. The easiest way is to add gum-out or something similar to the gas tank, and then run the engine.

I wonder how Norton Man would have spoken about the Kawasaki ZX-11D which was the sole possession of 19-year old Lance Corporal Marineguy. 130 rear-wheel hp (not accounting for the 10% ram-air boost at high speed) moving around 600 lbs at warp speed. Talk about reverence; I recited the Lord's Prayer as I pulled it off the dealer's lot and let the clutch out for the first time. My buddies and I made a trip from LA to Vegas on I-15. I guy on a GSX-R 750 pulled up along us and started pulling wheelies and gunning his throttle. We waved him off, declining his challenge. I waited till he was a 5 mile speck on the horizon of the straight desert highway, dropped it from 6th to 4th and gave him a 175mph fly-by. Man that machine was fun while it lasted. I can't believe it (or any open-class sportbike made since then) is even street legal. To drive it at posted speeds was like walking with no more than a 5-inch stride. Nowadays, when I get ideas about buying a motorcycle again (a cruiser this time, no need for speed anymore), my wife points at the three little boys playing outside, then to the 8" Z-shaped scar on my knee and says "Hell no." At least I can predict thunderstorms with my leg. Handy superpower for a pilot. Rbigg, Back on subject, I'd say pull the whole spindle and wheel off and take it to a garage (or neighbor) where they have an impact gun. It's amazing how something so simple like a lawn tractor tire can be the source of so much frustration. If you think taking a wheel off is a pain, just try replacing a tire on those little rims. Don't even think about attempting that without a large compressor, a valve core removal tool, and a ratcheting nylon strap.

Hmmm ... May 3 was a while back already. Just in case another person reads this, small engines tend to have a very fine mesh fuel screen in the tiny carburator. This tiny screen is the cause of many of the symptoms you speak of, and not easily removed and cleaned without damages. Keep in mind we are talking about a tiny carburator system most of us cannot inspect without a magnifier and "young" eyes. As to why the sparkplug is always replaced; old habit that is worth a few bucks to the mechanic. Besides, they are kind of cheap normally and avoid a lot of issues, or problems that might develop about 10 minutes after you get the machine home. The mechanic is thinking; Why take the chance with the old one? In any case, if you are serious about wanting to learn all you can about small engines, you want to give the local Voc Ed (now called Tech Centers) class/shop some serious thought. Normally the instructor has a lot of years of experience behind him or her when one speaks with the golden tongue for only a few coins of the empire from your pocket. If an adult, you might want to try out the night class for adults, and see if more training is desired later or not. One advantage most adult classes have over the day classes for high school students is you are required (more or less) to bring something in to work on, but the shop instructor can help with this also. You will be surprised how much you will learn without realizing you did. Needless to say the instruction pays for itself as a few years and projects pass successfully towards "repaired" by your hands.