Sounds like the ignition isn't working sometimes. I would check out any switch on it that controls the ignition. Look for loose, corroded or frayed wires at the switch. If you find a loose wire, fix it and it still does the same thing, it might be in the switch. I might for test purposes connect the wires around the switch and see how that works. Of course, you'll have to cut it off the old-fashioned way while that switch is out of the loop - wear heavy gloves and pull the spark plug wire. :) Maybe you can get a new switch or adapt another one to work. You're lucky that old rascal still runs at all. Most likely, repeated starting attempts flood it, which would account for the rough running when it does make contact.

Here is a typical flywheel key replacement. When you remove the shroud on top of the motor, blow it out with compressed air. A dust accumulation around the fins will cause overheating and coil failure. When you remove the flywheel nut, you can usually see if the key is sheared. Reprinted from a prior posting: The customer drops off a lawnmower with a tag that says “The motor stopped and couldn’t restart”. I pull on the starter rope and I hear a scraping noise underneath. The first step is to see if the blade is bent. The blade hub comes off at the same time. Since the blade is bent, along with a broken hub, and the motor won’t start, the usual culprit is the flywheel key being sheared. Unplug the spark plug wire. If you have electric start, disconnect the battery. The top dust cover is removed first, then the gas tank is emptied and removed. The oil fill tube mounting screw is removed and the fill tub is turned to the side, but still in place. The shroud is usually held in place with 4 bolts and after they are removed, lift the shroud straight up. At this point, you’ll have the flywheel in view. It’s obvious that the key is broken. Sometimes a motor will still run when the flywheel is this far out of alignment and sometimes a motor will not run when it is only slightly out of alignment. The flywheel puller tool (Briggs part number 19069) requires that two bolts be screwed into the flywheel. This is difficult without the use of a ¼” X 20 tap, and the flywheel is first tapped. You need at least 3 threads for the bolt to engage securely. Install the tool. There is a nut above and below the heavy steel bar. Turn the bolt into the flywheel until it bottoms out. It isn’t necessary to use the bottom nuts. Use a wrench to hold the bolt head and another wrench to turn the top nut down against the steel bar until it contacts. Do the same for the other bolt and nut. Alternate between the two nuts and turn the nut ¼ turn at a time until the flywheel pops off. When installing the new key, be careful that it doesn’t fall out of the shaft groove when placing the flywheel back on. You will need a suitable tool to hold the flywheel while you torque the center nut. I know that some will use a strong screwdriver to keep the flywheel stationary, but you might end up breaking one of the fins using that method. Sometimes the starter hub which goes between the nut and the flywheel has a tab on the bottom that engages a hole in the flywheel. If you torque to nut and the starter hub isn’t flat against it, the flywheel will break while being torqued. Always refer to a manual for the proper torque spec. Total job time: Less than ½ hour.

I know - its the kind of thing I like to do too. Sounds like the deck is okay. I would keep on using it. CD pack failures are irritating, but when you consider that most people have to buy a new mower long before 9 years, it seems very cheap to operate. Even if you have put new wheels and axles on at about the same frequency as the CD packs, you really are not spending any money on it. And, you can still find the rear-bagging kits and deck plates (blank for discharging, blocked for mulching). Other things you may encounter after such long service are crankshaft end seals popping out or just leaking, the need to rebuild the carb and carbon build-up in the exhaust ports and muffler. I always recommend adding Marvel Mystery oil to the gas in addition to your regular oil mix as well as the use of a fuel stabilizer. If you use Ethanol-blended fuel, get the Stabil Marine for Ethanol Fuels. All engines like MMO, in particular the 2-cycles.

In retrospect, I think the higher octane junebug recommended is a good idea in addition to the additives. I use mid-grade in my stuff. Just another note: If you partially release the engine/blade control bail from full speed until the ignition is cut off but the engine brake is not engaged, it is normal to have about a five to seven-second coastdown. These engines are not high-compression. To release the bail completely is supposed to stop the engine within two-three seconds. If yours were still 'popping' during the coastdown, it seems to me the duration would be extended. You mentioned ten seconds, but is that actually timed? Is that with the engine 'free' or with the brake on?