1973-kawasaki-g4tr-trail-boss_1

The lightweight trail bike was pretty well developed by the early 1970’s. The lightest and simplest were two-stroke oil injected machines, a step up from the workhorse early Honda Trail 55s and Trail 90s, step through designs made by the tens of thousands for decades.  The best designs also took the dual range transmission a step farther with a handlebar controlled internal dual range gearbox. This was unlike early Honda Trail 90s with which you had to switch to the larger rear wheel sprocket and add a length of chain to get into low range.

Though a bit of width and complexity was added with rotary valve induction, as opposed to typical port induction, Kawasaki and Bridgestone made this system work well on dual sport singles like the 350cc Big Horn and high performance Samurai twins. The rotary valve induction design had first been developed at MZ in East Germany, Walter Kaaden, engineer. With minor changes and different paint colors and graphics, the G4TR was made for almost ten years.

This Kawasaki G4TR Trail Boss is on loan from Rod Turner and is one of many off-road, trials and motocross bikes that will bring back memories when you visit the National Motorcycle Museum.

Specifications:

    • Engine: Two-Stroke, Air-Cooled Single
    • Bore & Stroke: 49.5mm x 51.8mm
    • Displacement: 99cc’s
    • Induction: Mikuni VM19SC, Rotary Valve
    • Ignition: Flywheel Magneto
    • Lubrication: Superlube, Port Injected
    • Compression Ratio: 7:1
    • Starting: Kick Starter
    • Horsepower: 11.5HP
    • Primary: Gear Driven
    • Clutch: Multi-plate, Wet
    • Transmission: 5-Speed, Dual Range
    • Electrics: 6 Volt
    • Frame: Tubular Steel
    • Suspension: Hydraulic Fork / Swingarm, Dual Shocks
    • Wheels / Tires: 3.00 X 18 / 3.00 X 18
    • Brakes: Drum, Front & Rear
    • Wheelbase: 50 Inches
    • Weight: 185 Pounds
7 replies
  1. rhip
    rhip says:

    Can someone explain the lever and dial knob on the right handlebar cluster? I assume one or both dealt with the dual range transmission. Did the system work well?

    Reply
  2. Mark
    Mark says:

    Thanks for your question, rhip.
    The “lever and black dial knob” on the right handlebar are the kill switch and the carb choke/enrichener.
    Looking at the 11th photo in the series here, on the left side of the bars, top to bottom are the high/low beam headlight control, the turn signal switch, the small round horn button and at the very bottom the high/low range control for the dual range aspect of the transmission, taking the five speed trans and making it a ten speed. I have no personal experience with this transmission operation but nothing on the several websites that discuss the bike complain about it’s operation. Thanks.

    Reply
    • Wally
      Wally says:

      This is the exact first bike I owned new when I was 14 years old. Loved it. At 61 years old I wouldn’t mind having one for old time sake.

      Reply
    • Treebeardzz
      Treebeardzz says:

      The hi-lo shift is accomplished by locking the alternate gear to a hollow shaft by locking 3 or 4(it’s been 42 years since I owned my 1st bike) balls with a plunger shaft, similar to how the push-button locks/releases a socket to a ratchet. The only time there is a problem is if you attempt to shift it under power(crunch)…..HOWEVER, If one is racing one’s brother who had a 250 Yamaha, you can quickly lock up the rear tire, clutch, up-shift to 3rd while simultaneously downshifting the auxiliary – without stopping – to climb a shortcut up a 40 degree hill(he had to take a longer route to where it was the 30 degree max that his faster 250 could climb) for a VERY satisfying “tortoise beats the hare” WIN. In low range, it would also tow a cute girl’s broken-down VW home using a borrowed section of metal cloths-line late one night.

      Reply
  3. Lotus
    Lotus says:

    Hey y’all, I managed to pick up one of these bikes off facebook market place for the right price and tend on fixing it up for a little fuel efficient zip around town rig. My biggest HAULT right now! Is that I don’t have a key. Does anyone know where I could find a new ignition cylinder with a key? it Doesn’t have to be oem. Or if y’all could help me hot wire or bypass the key. I would like to eveuntally be able to use all the bells and whistles that come with using the key! Thanks for the help y’all.
    -Lotus

    Reply
  4. John Martin
    John Martin says:

    The lever and black knob on the right handlebar are definitely for the ten speed hi/lo range function. The lever was turned with the transmission in neutral and the bike stopped to put it in low range. The black knob allowed you to shift to high range on the fly. I had this exact same bike from 1975 to 1978. put a million miles in the mountains of Montana with it. I wish I had one now, but I doubt it would carry my fat old butt!

    Reply

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