2007 Unison Desert Cat DS50 & DS90 ATV Service Manual

This Unison service manual covers the 2007 Desert Cat 50 and 90 ATVs, identified as DS50 and DS90, with horizontal two-stroke engines and automatic CVT transmission.

Searchable Service Text and PDF Contents

Text search and illustration detail: Service text is searchable, but the cover and some image labels are not. There are no embedded PDF bookmarks. The electrical test drawings are legible; the starter-relay photograph lacks the A–D terminal labels referenced in its test description.

Supplied as one printable 69-page PDF, including 66 pages of service information, one cover, one contents page, and one otherwise blank page numbered 31.

Engine, CVT and Chassis Service Coverage

These selected service topics sit alongside a maintenance schedule and air-cleaner element cleaning instructions.

• Engine repair: Engine removal and installation, cylinder and piston inspection, crankcase separation, crankshaft measurements, and bearing and oil-seal installation.

• CVT and final drive: Belt, roller and clutch inspection, driven-pulley disassembly, kick-start components, starter clutch, and final transmission gear service.

• Carburetion and lubrication: Auto-choke testing, float-chamber disassembly, fuel-height inspection, reed-valve checks, oil-pump inspection, control-cable adjustment, and air bleeding.

• Brakes and steering: Front drum brakes, rear drum and disc configurations, steering-knuckle inspection, tie-rod service, steering-shaft bearings, and rear-axle checks.

• Electrical diagnosis: Starting, charging and ignition fault finding, with A.C.G. generator, ignition-coil, starter-motor and starter-relay tests.

This manual suits mechanics and experienced owners familiar with engine measurements, electrical testing, and clutch work requiring a spring compressor.

Engine and CVT Repair

Top-end repair includes step-by-step removal and installation procedures, with checks for cylinder-head flatness, piston-to-cylinder clearance, ring end gap and piston-pin wear. Crankshaft procedures address connecting-rod clearances, runout measurement, bearing replacement and crankcase reassembly.

The cylinder inspection section provides a single bore service limit rather than separate DS50 and DS90 limits. It should not be treated as a complete source of DS90-specific cylinder wear data.

Piston-ring installation notes address ring orientation and the risk of damaging the piston and rings during assembly. CVT inspection extends to the clutch housing, lining, movable faces and driven-face spring, with different spring specifications listed for the two engine sizes.

Mikuni Carburetors, Oil Injection and Cooling

The specification table identifies the Mikuni M1A for the DS50 and M2A for the DS90. Carburetor procedures cover throttle-valve and jet-needle inspection, starter-plunger continuity and airflow tests, float-chamber service, and air-screw and idle adjustments.

Starter-plunger test illustrations show the auto-choke test arrangements. Reed-valve coverage includes removal, stopper-height and flatness checks, and installation.

Oil-injection service covers pump removal, external inspection, control-cable adjustment and air bleeding. The manual warns that dismantling the oil-pump body can damage it; an internal pump rebuild is outside this section’s scope.

A cooling-system section view illustrates the fan and airflow through the cylinder and head fins.

Brake Variants, Steering and Chassis

Rear-brake coverage distinguishes drum, hydraulic disc and mechanical disc assemblies through separate parts drawings and service illustrations. Disc-brake procedures cover removal, pad and rotor inspection, and installation; hydraulic brake bleeding is not included.

Front-wheel and steering exploded views accompany brake-panel, steering-knuckle/front-spindle and tie-rod service. Inspection data cover the knuckle bushings, steering-shaft sleeve and bearing, rear-axle runout, and sprocket condition. Bodywork and exhaust removal are also illustrated.

Maintenance references identify SAE90 gear oil and the NGK BPR8HS spark plug, with brake-lever free-play data, chain and toe-in adjustments, and torque specifications for cylinder-head and chassis fasteners.

Electrical Tests and Fault Isolation

The no-start and poor-running flowcharts separate fuel delivery, spark and compression checks. This helps narrow the likely source of a fault before choosing an engine, carburetor or ignition repair procedure.

Electrical reference data cover the A.C.G. stator and exciter coil, ignition-coil resistance and output, starter operation, and relay continuity. Coil-test connection drawings and a starter-motor test illustration support these checks. The CDI module appears in troubleshooting, but the manual does not include an internal CDI repair procedure or a complete vehicle wiring diagram.

Observe the manual’s precautions for gasoline, battery acid, exhaust fumes and hot exhaust components when carrying out service.

A Preview of CVT Wear Limits

The CVT inspection section lists a 14.6 mm drive-belt width service limit and a 14.5 mm roller outside-diameter service limit. Both appear beside the corresponding measurement illustrations.

Clutch inspection data give a lining-thickness service limit of 1 mm, with separate checks for clutch-housing diameter and driven-face spring length.