Hi! I'm new to this site, and trying to repair my lawnmower engine - it is a Tecumseh TVS-600 (this is stamped on the side). A good parts diagram for the engine is shown here: (the ignition system is very basic, with just a coil and a magnet on the flywheel which goes past the coil, and a HT lead to the sparkplug, and a single wire that goes to the on/off/engine speed selector) http://www.partstree.com/parts/?lc=tecumseh&mn=25-TVS600-661&dn=ETVS6001661-25-EN It had some problems, where it would become difficult to start when it had been used for a while, unless it was left to cool down, but otherwise, it ran smoothly, and started easily. It was used by someone (not myself), and it made a funny noise, so they stopped using it. It turned out the blade had half-loosened, such that it would have spun around 180 degrees before the crankshaft caught up with it again - this would have caused sudden changes in the speed of the engine for sure. I then tightened the blade, tried to start it, and it kicked back very badly, pulling the starter cord out of my hand. It kept doing that every time I tried to start it (in fact, it would run backwards for a while, by doing the kick-back, and then turning backwards slowly, but just fast enough, so it would keep running (barely) backwards. I have done the following tests / investigation to find out what might be wrong: (1) I noted that, when it did the running backwards thing, even if I switched the speed setting to 'Off', it would still keep running backwards, for 10-20 seconds, slowly. (2) Checked crankshaft (the blades side of the crankshaft) and it isn't bent at all when spinning it. Also, it spins freely when sparkplug is out, no catching / resistance etc. (3) Removed flywheel and checked flywheel key - it is in one piece, and hasn't shifted. It is very, very slightly worn, but I don't think this would be causing the current problem or the issue in (4) below (4) Removed sparkplug and checked where TDC is using a screwdriver to detect the piston movement. Rotating the engine slowly using the flywheel, the magnet passes the coil when the compression stroke is *just* starting (a few degrees of compression has occured). Actual TDC occurs about 88 degrees *after* the magnet has passed the coil. (5) Checked compression - this is good (no compression tester, but at least as good as any other working lawnmower engine / other small engine I have used in the past, and probably better) Any ideas on how to proceed next, or what might be wrong? I was wondering if the crank was twisted, but, it is quite a short crankshaft, (see the diagram in the link above) and it is quite thick; I can't imagine it could twist 90 degrees without damaging the flywheel key, and without any bending of the crankshaft occuring at all? Thanks for your advice - will keep looking at the engine and see if I can figure it out but would be grateful if anyone could help me with this!