1971 Yamaha AT1-MX 125cc

Welcome to the 1971 Yamaha AT1-MX 125cc MX Forum. Feel free to post anything related to this model in the category. Anything new, will be added to this section. If you see any errors, please contact me privately. There were many errors, in the early Yamaha literature. I will make some error's of my own.

                     1971 Yamaha AT1C-MX Specifications

            Model 1971 Yamaha AT1C-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 Yamaha AT1-MX Store is Located: CLICK HERE