If you have the DBG or JDB pump on your engine - there is only one special tool needed to work on it yourself. A "Bristol Wrench" to get the head screw out. You can find new for around $10. A $10 plastic timing window is nice to have to check the automatic advance on the running engine but not 100% necessary (cost $10). A 2" outside mike can be used to check or set max fuel delivery.
I doubt your metering valve is the problem unless it's worn out. I'd be more apt to think the linkage that operates the metering valve is loose or full of debris from a shattered pellathane weight dampener.
You can get the Deere-Stanadyne manual for free on-line in PDF. New parts costs comes to $15 for a complete seal and o-ring kit. $10 for a new metering valve, $6 for a housing-pressure-regulator, $8 for a new pilot tube, $15 for a new vane-pump kit, and an extra $55 if you want to upgrade the pump and eliminate the plastic-pellathane ring forever.