I just did mine recently. Depending on how mechanically inclined you are, it is pretty straight forward. I thought it was very easy. I actually enjoyed doing it. After a compression test that showed about 155 on every cylinder which seemed good to me. I first bought an overhead valve spring compressor at sears for like 15 bucks. Kinda looks like a gear puller, or flaring tool, also bought a magnetic tipped telescopic $5 pickup tool it will make your life easier with the keepers, it's about the size of a pen but looks like an auto antenna. Then I went to the local parts store and bought the seals, which they took like a day to get, and a valve cover gasket, and a carb spacer-to-intake gasket. Then I removed the valve cover. I'd remove the carburetor too, to make it easier. Remove the rocker assembly or rockers whichever your model has, then remove the push rods, making sure lay them where you know to put them back as they were. Cover all the pushrod holes, oil return holes, and intake hole with a clean rag, then one by one, I removed a spark plug, rotated the engine by hand until the piston was as high as it would go looking down with a good flashlight and then stuffed as much 1/4 inch nylon rope as would fit in there with a long slim screwdriver being careful not to scrape the piston, about at least a foot. Once that's done I compressed the spring with the tool, then I had to tap the sleeves with a screw driver, some people recommend a box end wrench, but it was just a couple taps, if they're really stuck I'd use the box end wrench so you don't damage the sleeves with screwdriver. After that, you can slide the spring with sleeve down and use the magnetic tool to pick up the keepers one half at a time. Remove the spring and place it right side up with the compressor still on it where you won't lose the sleeves. Place the keepers somewhere safe too as they are tiny. remove and replace the seals. Check the valve stems for play, and reverse the process. Never forgetting to raise the piston and stuff the rope for each one, after you replace the spark plug and wire for the last one you did. I'd use a garage. Think slow, and don't get intimidated--I had no idea what a keeper looked like or how they held on, but as soon as I did the first one, I figured it out real quick. In the end I can say it was very satisfying as it seemed to cure the problem.
