Welcome to the 1971 Yamaha AT1-MX 125cc MX Forum. The factory Paint color was called: Brilliant Red & the vin number range was" AT1-313101 to 317191. Feel free to post anything related to this model in the category. Anything new, will be added to this section.

       1971 Yamaha AT1-MX Specifications

Model 1971 Yamaha AT1-MX

   Dimensions:

Overall Length 76.4 In. / 1,940MM

Overall Width 35.8 In. / 910MM

Overall Height 42.9 In. / 1,095MM

Wheelbase 50.8 In. / 1,290MM

Min. Ground Clearance 9.1 In. / 230MM

    Weight:

Gross 218 Lbs. / 99KG

Net 202 Lbs. / 92KG

   Performance:

Max, Speed 60 MPH +

Fuel Consumption 114 MPG @ 25 MPH

(On paved level roads)

Climbing Ability 30 Degree

Min. Turning Radius 74.8 In. / 1,900MM

Braking Distance 58.3 Ft. @ 31 MPH

   Engine:

Model AT1

Type 2 Stroke, Gasoline

Lubricating System Separate (Yamaha Autolube)

Cylinder Single, forward inclined 5 Port

Displacement 7.51 cu. in. (123cc)

Bore X Stroke 2.205 X 1.969 In. (56 X 50MM)

Compression Ratio 7.1:1

Max Power 18.2 BHP/8,500 RPM

Max Torque 11.4 Ft.-Lbs/7,500 RPM                               

Piston Skirt Clearance .0016 - .0020 In. / 0.40 - 0.50MM                                         

Starting System Primary-Coupled Kick

Ignition Timing B.T.D.C 2MM +/- .1MM

NGK Spark Plug & Gap B-9E 0.5-0.6 MM

Contact Break Point Gap 0.016 - 0.020 Inch / 0.40 - 0.50 MM

Volt Reg. Adjustment -

(Volts @ RPM - No load)

Cutout Relay Adjustment -

Condenser Capacity .22UF +/- 10% (Microfarad)

   Carburetor:

Type VM26SH

Main Jet # 190

Jet Needle 4F15 - 2

Air Jet 0.5

Needle Jet 0 - 2

Cut Away 1.5

Pilot Jet # 30

Air Screw (turns out) 1 1/2

Starter Jet # 40

Float Level 25.5MM

  Intake:

Air Cleaner Wet, Foam Rubber

   Transmission:

Clutch Wet, Multiple Disk

Primary reduction system Helical Gear

Primary reduction ratio 3.894 / (74/19) Teeth

Trans Oil Capacity .80 Qts

   Gear Box:

Type Constant Mesh, 5 Speed Forward

1st Gear teeth & Ratio 2.833 (34/12) 33.10

2nd Gear teeth & Ratio 1.875 (30/16) 21.90

3rd Gear teeth & Ratio 1.368 (26/19) 15.98

4th Gear teeth & Ratio 1.091 (24/22) 12.76

5th Gear teeth & Ratio 0.957 (22/23) 11.18

Secondary reduction system Chain

Secondary reduction ratio 3.000 (45/15)

  Chassis:

Frame Tubular-Double Loop

Front Suspension System Front Telescopic fork

Rear Suspension System Swinging Arm

Fork Oil Capacity 160cc (5.4 Oz.)

Front Cushion System Coil Spring / Oil Damper

Rear Cushion System Coil Spring / Oil Damper

  Steering System:

Steering Angle 49 Degrees both left & right

Caster 60.5 Degrees

Trail 4.84 In. / 123MM

  Braking System:

Type of brake Internal Expansion

Front Operation System Right hand operation

Rear Operation System Right foot operation

  Tire Size:

Front 3.25 - 18 - 4PR Knobby

Rear 3.50 - 18 - 4PR Knobby

Front Tire Pressure 14 P.S.I

Rear Tire Pressure 17 P.S.I

  Oil Pump:

Adjustment Stroke Min 0.20 - 0.25 MM

Adjustment Stroke Max 1.85 - 2.05 MM

  Dynamo:

Model GS-114

Manufacturer Hitachi Ltd.

  Battery:

Model -

Manufacturer -

Capacity -

 Lighting:

Head Light -

Tail Light -

Stop Light -

Meter Light -

High Beam Indicator Light -

  Tanks:

Gasoline Tank Capacity 1.9 Gallons

Oil Tank Capacity 1.3 Quarts

  Chain:

Tension (Up & down free play) 20MM (25/32)

The 1971 Yamaha AT1-C Rider's Manual is Located: CLICK HERE

The 1971 Yamaha AT1-C Service Manual is Located: CLICK HERE

The 1969-1971 Yamaha AT1-CT1-MX Combined Service Manual is Located: CLICK HERE

The 1969-1971 Yamaha AT1-CT1 Combined Parts Manual #1 is Located: CLICK HERE

The 1971 Yamaha AT1MX Parts Manual # 2 is Located: CLICK HERE

1971 Yamaha AT1-MX Autolube adjustment and color codes are Located: CLICK HERE

The USA 1971 Yamaha AT1-MX Brochure is Located: CLICK HERE

1971 Yamaha Full Line Up Brochure: CLICK HERE

The 1971 Motorcycle & Trail Bike Handbook is located: CLICK HERE

1971 Yamaha AT1MX Parts CLICK HERE