Well, you need to for certain make sure it's getting good fuel supply. Fuel filters are rather cheap, so no big loss replacing it. Typically, buy not definitively, when you have a fuel restriction, such as clogged filter, if the motor will run smooth at idle it will at least rev just a bit, but won't work under load hardly at all. If it runs smooth at idle, you may have a broken governor control spring on the throttle control. Go through your fuel supply system first before looking into governor control.
Have you checked that the shutoff valve on right side behind cab is fully open? Check to make sure air bleed knob valve on fuel return line connection to injection pump is fully closed? Check to make sure lift pump is sending fuel to injection pump?
