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Hi, my name is***** the fuel shut off diaphragm is installed incorrectly it will cause the motor to run wide open. Remove the shut off valve and cover the opening and see if it still runs away. The hook arm on the shut off valve needs to engage into the linkage in the pump. If it is installed wrong it will push the linkage to the wide open throttle position.
Let me know if this is the problem.
Correct, the engine will run away if there is excessive blow by or if the pump is defective but the usual problem is with the shut off diaphragm. It's also possible that the rack in the pump is seized. I think it will still run 180° out.