It would likely be your throttle able adjustment or the linkage got bent in the front.(happens enough on these)Assuming the spring doesn't look damaged and is connected, and the cable adjustment is ok. Adjust the linkage. The linkage will adjust by bending the tab forward or it will have a torx screw on the front. In the perfect world, you would have a tach- but adjust by engine sound err on the cautious side rather than overspeed.

Thanks - the linkage has gotten bent a couple of times. I'll give it a try when the weather clears.

Well, weather cleared up, straightened out the linkage and speed did come up. Now it won't take load. As soon as it hits heavy grass, it dies. It's like the governor isn't working. The spring is in place and all the linkages are intact. The governor seems to be hunting somewhat with no load.

The hunting of the governor would indicate that it is running a bit lean. Ensure that the intake is tight and the gasket and new seal is in place. If the seal wasn't new before, make it new. Be sure that the carb mounting bracket has all its bolts in it. The older models had a HS adjustment screw just above the float bowl towards the front of the engine. Turn it out 1/4 turn and fine tune from there. Fuel also needs to be fresh- hopefully w/in 1 month old. If all that seems in order re-clean the entire fuel system complete.