from our e-mails:
Q:  I have a John Deere 140 that I've owned since new.  It starts to stall, like bog down to the point of stalling.  Could a hydrostatic pump malfunction be pulling the engine down? It bogs even when I turn the mower off, move the forward and reverse lever,  but it starts to recover if I pull the throttle back.  I'm stumped.
A:  I think you are getting a carbon glow in the combustion chamber and it is causing a pre ignition before the spark plug ignition fires.
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