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Luke, it could be either the carb or the governor but the usual cause is the carb. Does running with the choke partially on help, or slow the surging? If so, suspect the carb. ~Try disconnecting the throttle rod at the carb & operating the carb by hand to see if the engine runs smoothly when operating the carb by hand [if it doesn't suspect the carb, if it does suspect the governor]. ~Make sure the throttle rod from the governor to the carb isn�t rubbing or binding on anything & the cotter pin in the linkage hole isn�t hitting the carb throttle shaft housing. With the engine off, operate [move] the rod between the governor & carb by hand & see if you can feel it binding or sticking. ~Run a fuel flow test; open the carb bowl drain & see if you have a pencil sized stream of fuel for AT LEAST 30 seconds [if not find out why]...Note: if your tractor has an oil pressure operated fuel shut off you will have to un-screw the knurled nut on it & hold the pin in to do a fuel flow test. If you don�t have a good fuel flow check the tank fitting, tank mounted strainer & inlet screen in the carb. ~Check the air cleaner & intake tract for restrictions, a plugged air cleaner or intake snorkel will effect the engine operation. ~Make sure the exhaust heat control valve is turned to either HOT or COLD & not in between. ~If all above checks out ok try a new set of spark plugs, maybe you have a cylinder firing intermittently causing a surge.
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