Welcome to the 1971 Yamaha HT1B-MX Forum. Feel free to post anything related to this model in the category. The factory color was called Competition Yellow. The USA Vin range was HT1-000101 to 023405. 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 HT1B-MX Specifications

            Model 1971 Yamaha HT1B-MX

   Dimensions:

Overall Length 73.4 In. / 1,864MM

Overall Width 35.4 In. / 900MM

Overall Height 40.9 In. / 1,038MM

Wheelbase 48.4 In. / 1,229MM

Min. Ground Clearance 9.1 In. / 231MM

    Weight:

Gross 192 Lbs. / 87Kg

Net 181 Lbs. / 82Kg

   Performance:

Max, Speed 55 MPH / 95Km/h

Fuel Consumption 164.5 MPG @ 25 MPH / 70Km @ 40Km/h

(On paved level roads)

Climbing Ability 32 Degree

Min. Turning Radius 68.9 In. / 1,750MM

Braking Distance 23 Ft. @ 22 MPH (7M @ 35Km/h)

   Engine:

Model HT1

Type 2 Stroke, Gasoline

Lubricating System Separate (Yamaha Autolube)

Cylinder Single, forward inclined 5 Port

Displacement 5.43 cu. in. (89cc)

Bore X Stroke 1.969 X 1.795 In. (50 X 45.6MM)

Compression Ratio 8.1:1

Max Power 14 BHP/9,500 RPM

Max Torque 7.96 Ft.-Lbs @ 9,000 RPM                        

Piston Skirt Clearance .0016 - .0018 In. / 0.40 - 0.45MM                                         

Starting System Primary-Coupled Kick

Ignition Timing B.T.D.C 2.5MM

NGK Spark Plug & Gap B9-EN 0.5 MM

Contact Break Point Gap 0.012 - 0.015 Inch / 0.30 - 0.4 MM

Piston Ring End Gap 0.15 - 0.35 mm (single ring)

Condenser Capacity .22UF (Microfarad)

   Carburetor:

Type / ID VM24SH / 276 MI

Main Jet # 130

Jet Needle 4DH7 - 2

Air Jet -

Needle Jet N - 8

Cut Away 2.0

Pilot Jet (#) 30 / 0.6

Air Screw (turns out) 1 1/4

Starter Jet (#) 40

Float Level 22.5MM

Valve Seat 2.0

  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 650 - 700cc / .69 - 0.79 Qts

   Gear Box:

Type Constant Mesh, 5 Speed Forward

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

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

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

4th Gear teeth & Ratio 1.090 (24/22)

5th Gear teeth & Ratio 0.956 (22/23)

Secondary reduction system Chain

Secondary reduction ratio 3.714 (52/14)

  Chassis:

Frame Tubular-Double Loop

Front Suspension System Front Telescopic fork

Rear Suspension System Swinging Arm

Fork Oil Capacity 132cc - 147cc (4.5 - 5.0 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 4.5 In. / 114MM

  Braking System:

Type of brake Internal Expansion

Front Operation System Right hand operation

Rear Operation System Right foot operation

  Tire Size:

Front 3.00 - 18 - 4PR Knobby

Rear 3.25 - 18 - 4PR Knobby

Front Tire Pressure 14 P.S.I / 1.0KG/cm2

Rear Tire Pressure 17 P.S.I / 1.2KG/cm2

  Oil Pump:

Adjustment Stroke Min 0.20 - 0.25 MM

Adjustment Stroke Max 1.85 - 2.05 MM

Mix Ratio With & Without Pump 30:1 / 15:1

  Dynamo:

Model F130-04

Manufacturer Hitachi Ltd.

  Battery:

Model -

Manufacturer -

Capacity -

 Lighting:

Head Light -

Tail Light -

Stop Light -

Meter Light -

High Beam Indicator Light -

Flasher Light -

  Tanks:

Gasoline Tank Capacity 1.7 Gallons (6.5 Liters)

Oil Tank Capacity 1.3 Quarts (1.2 Liters)

  Chain:

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

Wanted 1971 Yamaha HT1-MX Rider's Manual. If you have this manual for sale, or wish to donate a copy, we want this manual, for the digital library.

The 1971 Yamaha HT1BMX Service Manual Supplement is Located: CLICK HERE

The 1971 Yamaha HT1 Primary Service Manual located: CLICK HERE

The 1971 Yamaha HT1BMX Parts Manual Supplement is Located: CLICK HERE

The Primary HT1 Parts Manual is Located: CLICK HERE

The 1971 Yamaha HT1B Article is Located: CLICK HERE

The 1969-1971 Yamaha Autolube Adjustment & Color Codes are Located: CLICK HERE

The 1971 Yamaha HT1-BMX Brochure is Located: CLICK HERE

1971 Yamaha Full Line Up Brochure: CLICK HERE

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

The 1971 Yamaha HT1BMX Store is Located: CLICK HERE