I知 having a problem with a MTD 522 log splitter. Motor binds and stalls when under a load. I changed the coupling and spider gear. I haven稚 run any pressure test. It will start splitting, then bind and stall the motor.
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Could be the Governor. Google engine governor. I had the same issue with a tiller. Governor linkage had come loose and it would run perfect until the tines touched the soil then it would bog and die.
Is the carb mixture adjustable? Sometimes the jets get partially blocked with gum from the gas and it will have no power. Maybe you could open the jet a little or clean the carb. I don't know if that's the problem, just a suggestion.
If this is a Hi-lo log splitter pump is it possible the sequence valve for shifting from hi to low is stuck or malfunctioning. Like John states, you need to determine if this is an engine problem or a hydraulic problem.