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The rope snatching is an indication of a sheared flywheel key. It is over advanced (ignition timing). Pull fly wheel and use a steel replacement key. Original key was probably aluminum. The valves a adjusted cold with the valve closed, set with a slight shake present at rocker arm and valve stem.
The timing is fixed, if you suspect the timing is off the only adjustments available are the .030 clearance from pickup to flywheel and the shear Key that positions the flywheel on the crankshaft. You would also want to make sure your valve clearance is .030 as well, the issue sounds like a valve leaking, a dead cylinder or mal adjusted valve clearance causing the exhaust valve to hang open just a bit.
This is a true tale sign of a valve being out of adjustment or possible burnt or sticking. Most likely its just out of adjustment. Setting them to Book Specifications of: Valve Clearance (cold) IN and EX .005" (0.13 mm) should take care of the problem. Since you said that it runs fine rules out the possibility of a sheared flywheel key, though I have seen one run with it slightly sheared. Thanks; George
It could be as simple as a sheared flywheel key and/or the valves needing adjustment. The OHV engines that come in lawn and garden equipment these days are notorious for being very picky about the correct valve settings, especially single cylinder engines. Another common problem involves the fuel inlet valve in the carburetor. Not the solenoid valve but the float valve inside - if it doesn't seat properly fuel will overflow the carburetor and enter the engine. Several bad things happen after that - the cylinder can get enough gasoline in it to lock the piston when you try to start it and that can result in the aforementioned sheared flywheel key. The gasoline will also get past the piston and into the crankcase where it dilutes the oil and the result is poor lubrication. one of the first components to suffer from the lack of lubrication is the camshaft, particularly the exhaust valve lobe, which wears down to the point that it does not open the exhaust valve far enough and the exhaust cannot be expelled fully on the exhaust stroke. The leftover gasses then escape from the engine through the carburetor when the intake valve opens, sounding like a backfire but rather than fire coming out the carb you get popping and raw gas blowing out the intake. Check your oil for the odor of fuel. If it smells like gasoline and, perhaps is inexplicably overfilled with oil according to the dipstick, plan on having the carburetor inlet needle and seat replaced, possibly the flywheel key replaced and probably the camshaft replaced. Keep your fingers crossed that it is just the valves needing adjustment.
It sounds like the key way worn, tweaked a bit eg: shear pin. You have to pull the top cover, fly wheel cover. remove the fly wheel and replace the key way.
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