Cockshutt 540 throttle troubles

Recently required a rebuilt Cockshutt 540. I have noticed that it seems to easily start and can sometimes run for hours but other times it is a true buggar. The tractor will run and then start running roughly and will quit unless you quickly pull the choke and release. I have the throttle switch pulled down and it seems to gradually work itself back down reducing the speed but that is another issue. I noticed that the throttle arm that connects from the throttle cable to the carb rocks when it is starting to run roughly (please see link) and this can happen on flat ground as well as hilly territory. I read through some of the forums and I was told that this is a gas issue...so I checked the gas line and sure enough a steady stream of gas is running through the line. The carb bowl was cleaned out as well but that still does not solve it.

I've been told that it could be the govenor or that there could be a hole in the float in the carb. My question is where should I go from here...has anyone else with a Cockshutt had a simular problem? The carb is a Zenith.

Thanks very much in advance...newbie here so don't be too harsh :)

• pics of the throttle arm to the carb