(quoted from post at 17:34:47 04/07/13) It may be a lean condition as others have stated. If it will pull a heavy load good for an extended period of time without the manifold starting to show red, forget the lean. It takes a while under load though to prove this out. A worn out goveror doesn't make them lope unless parts are sticking. A good active governor is much more prone to lope (surge) than a worn one. Notice the square machined spot on the lower rear corner of governor housing. Well, IH had some H tractors that were prone to surge so they made a surge adjustable screw available and it goes in that spot. It is not drilled. I have only seen two in my life (41 years working at IH dealer) and one of them is the 45 H my dad bought new and I have now. I don't know if it was on there when he bought it or installed later. IH did a couple other things to over come surgeing on different engines, but I don't remember them doing it on an H. The throttle butter fly is not exactly centered on some carbs and the degree number on the butter fly shows this and also the butterfly is beveled on the edges. Opposite on each side and has to be installed properly to operate correctly.
Just some extra things to think about. And, also, ethanol runs a little leaner so you may have to increase the main jet just a couple thousands. The gasoline engine main jets were pretty close to what became knows as a fixed jet in later years and main jets don't come with carb kits. Neither do air bleeds.

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