Part of the Kubota Repair Manuals.
This is the Kubota Workshop Manual for the Z122E-AU, Z121S-AU, Z125E-AU and Z125S-AU zero-turn mowers, covering machines built around the GH731V-1, GH736V, GH733V-1 and GH750V engines. It runs 172 pages and is delivered as a downloadable PDF you can read on a phone, tablet or computer, or print for the shop.The manual walks through the whole machine: engine structure and lubrication, the hydrostatic transaxle, front axle, lift system, the full electrical system with wiring diagrams, and the mower deck. You get identification details, troubleshooting, servicing specifications, tightening torques, and step by step disassembly and assembly.With it you can diagnose a non-starting engine, service the electric PTO clutch, chase a weak drive side, level the deck, or rebuild a worn front caster, all backed by Kubota's own procedures and spec values.
What's Inside This Kubota Z121–Z125 Series Manual
| System | Pages | Key Topics |
|---|---|---|
| Information | 4-15 | - |
| General | 16-65 | Identification, Serial Number, Cylinder Number, General Precautions, Wiring, Battery, Fuse, Connector |
| Engine | 66-82 | Z122E, Z125E, Z121S, Z125S, Fuel System, Fuel Line, Lubrication System |
| Transaxle | 83-112 | Hydraulic Circuit, External Components, Inner Components, Parking Brake, Overall Transaxle Reduction, Separating Transaxle, Removing Control Lever Panel and Fuel Tank, Removing ROPS |
| Front Axle | 113-119 | Separating Front Wheel and Wheel Bracket, Front Wheels Wander to Right or Left, Flange Nut (Wheel), Bracket Bolt, Remove Wheel Bracket |
| Lift System | 120-127 | Cam Dial, Cam Shaft, Cam, Front Lift Shaft, Rear Lift Shaft, Link Stopper, Mower Link |
| Electrical System | 128-154 | Wiring Diagram, Start System and Opc, Start System, Operator's Presence Control, Safety Switches, Relay, Electrical Equipments |
| Mower | 155-172 | Power Transmission, Mower Deck, Anti-Scalp Rollers, Blades, Mower Belt, Tension Pulleys, Blade Shaft, Pulley Holder |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| All Models | ||
| General Use Screws, Bolts and Nuts (M6, No-grade or 4T) | 7.9 to 9.3 N·m | p. 27 |
| General Use Screws, Bolts and Nuts (M8, No-grade or 4T) | 18 to 20 N·m | p. 27 |
| Fuel tank capacity | 16 L | p. 26 |
| Engine crankcase (with filter) capacity | 1.8 L | p. 26 |
| Rated engine revolution | 3600 rpm | p. 13 |
| Engine crankcase oil capacity | 1.8 L | p. 13 |
| Transmission case oil capacity | 4.8 L | p. 13 |
| Z122E, Z125E | ||
| Engine oil change interval | every 50 Hr or every 1 year | p. 30 |
| Z121S, Z125S | ||
| Engine oil change interval | every 100 Hr | p. 31 |
| Z122E-AU | ||
| Max. engine power (Gross) | 16.4 kw (22 HP) | p. 13 |
| Z121S-AU | ||
| Max. engine power (Gross) | 15.7 kw (21 HP) | p. 13 |
| Z125E-AU, Z125S-AU | ||
| Max. engine power (Gross) | 18.6 kw (25 HP) | p. 13 |
Kubota Z121–Z125 Series Common Problems This Manual Covers
Electric PTO clutch will not engage blades
The blades fail to spin when the PTO switch is pulled, often because the electric clutch coil is out of its 2.88 to 3.18 ohm resistance range or a safety circuit is open. The Electrical System section covers clutch testing and the start and OPC circuits.
Manual Section: Electrical System p. 128Uneven cut or deck vibration
A rough or stepped cut usually points to a bent blade, worn spindle, or a deck that is out of level. The Mower section gives servicing specifications, blade bolt torque, and the checking and adjusting steps.
Manual Section: Mower p. 155Weak or uneven hydrostatic drive
One side pulling or a general loss of drive power is a common transaxle complaint, tied to the hydraulic circuit, internal components, or the parking brake. The Transaxle section covers structure, reduction, and servicing.
Manual Section: Transaxle p. 83Hard starting or engine oil issues
Hard starting and low power can trace back to the fuel line or a lubrication problem. The Engine section documents the structure, fuel system, and lubrication system for each model variant.
Manual Section: Engine p. 66Front caster play or bearing wear
Wobble or excessive play in a front caster wheel usually means worn wheel bearings or a loose wheel bracket. The Front Axle section provides troubleshooting, tightening torques, and disassembly and assembly steps.
Manual Section: Front Axle p. 113Deck height or lift linkage problems
Trouble raising the deck or holding a set cutting height points to the lift linkage. The Lift System section covers troubleshooting, tightening torques, checking, and disassembly and assembly.
Manual Section: Lift System p. 120Frequently Asked Questions
Which Kubota mowers does this manual cover?
It covers the Kubota Z122E-AU, Z121S-AU, Z125E-AU and Z125S-AU zero-turn mowers in one 172-page workshop manual, so the same document serves all four model variants.
What engines are covered?
The manual covers machines with the GH731V-1, GH736V, GH733V-1 and GH750V engines, documenting engine structure, the fuel system, and the lubrication system in the Engine section (page 66). p. 66
Does it include wiring diagrams and electrical troubleshooting?
Yes. The Electrical System section (page 128) includes the wiring diagram plus the start and operator presence control circuits, charging system, hour meter, and head light and PTO clutch coverage. p. 128
What is the mower blade bolt torque?
The blade bolt torque is 103 to 118 N·m. This and the other servicing specifications for the deck are given in the Mower section (page 155). p. 155
How quickly can I access this manual after buying?
You get a 172-page searchable PDF that downloads instantly after checkout. Open it on your laptop, tablet, or phone, bring it right to the shop floor.
Are there any print restrictions on this manual?
No restrictions at all. Print individual pages, full chapters, or the entire manual. The PDF is completely unlocked.
Can I find hydraulic circuit diagrams in this Kubota Z121–Z125 Series manual?
Full hydraulic system diagrams are included, covering circuits, valve locations, and hydraulic component specs for the Kubota Z121–Z125 Series.
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