Does anyone know of a way to test the governor? Lately my 4240 doesn't seam like the governor wants to advance the throttle when the engine starts to bog down. It could be nothing but it might be an issue. I know the fuel system up to the filter is fine and I don't see any change in the smoke (and the air filters are clean) so I don't think there's an issue getting air. But when I rev the motor up to 2800 it seams to be real easy to bog the engine down. Normally I don't need to run that high (2000~2400 rpm range) so I can't say I know what's normal. I did look at the parts diagram so I know approx how the system works. It looks like the throttle is connected to the governor with two springs but I'm not sure how the governor connects to the injection pump. I think it connects to the fuel cam shaft but that part isn't clear. I have been pretty lax about getting the work shop manual but I guess I'll pick one up. Anyway I would rather deal with a potential issue now, in the warmth of summer than in the dead of winter (assuming it has an issue).
In a nutshell, the governor controls the fuel rack movement to maintain the engine speed. A set of engine driven flyweights opposes a spring attached to the throttle lever. As load decreases and the engine speed comes up, the flyweight force overcomes that spring pressure and reduces the fuel rack setting. As load increases and engine speed drops, the spring overcomes the reduced flyweight force and increases the fuel rack to bring the speed back up.
It does that at any load from zero to whatever the engine is capable of putting out, less parasitic loads like alternator, A/C, water and hydraulic pumps, etc. They can be tested, but it's not easy. A PTO dynamometer can load the engine to varying degrees, I'd say yours is probably rated at 35-37 PTO HP. A dealer is going to be the only place to find something like that, unfortunately. Unless the engine is in poor condition, which I doubt, they can be pretty bad before they won't develop full HP.
With a mechanical governor there is always some speed droop inherent in the system. In short, there will be a minor decrease in controlled engine speed when you increase load. For example, if you're bush hogging a field and the engine speed is 2400 with the cutter just turning freely, I wouldn't be surprised to see it drop a hundred or more RPM when it's under heavy load, and maintain that speed until the load drops again. If you overload it, the speed will simply decrease until the load decreases or the engine stalls.
I assume your tractor is HST? Does it have the ATA? (Auto Throttle Advance) If it does, that may not be working properly, if at all.
You didn't say what you were doing when you noticed the drop in speed. PTO work or simply moving the tractor? Some of the HST tractors are working hard in the higher speed ranges, I know of one gent with a GL3240 that was surprised at how much the ground speed fell off when climbing a hill in high gear at road speeds. They simply don't have the horsepower to drive that much weight up a hill at that speed.
My gear drive
L3400 will run at full governed speed (~2800 rpm or a bit higher) in high gear on a flat road, but throw a hill in front of it and the rpm drops to about 2600. Downshift and the rpm comes right back up as the ground speed drops.
