Replica KOSO speedo install GS125

[linuxrob]

GS125 Speedo replacement

There now follows the usual rambling, oversimplified, and photo overloaded waffle documenting the latest job done on a wet afternoon in the shed as it's wet and there's nothing on the telly.

The GS125 tacho has never worked thanks to a shattered drive worm gear (previous botcher) and the speedo sticks occasionally after the heard of cows incident winter 2015. I will to kill 2 birds with one stone, so to speak, and fit a new combination unit. A Koso RX-2N+ copy from China

eBay listing

 

It arrived in less than a week, and included this wiring diagram.

 

The connector plugs on the unit are a standard 2.8mm blade type 2 male and female 9 way addition ones were bought for the dash lights from eBay and one 8 way 2.8mm one for the gearchange multiplug on the GS125.

 

From the GS125ES manual I made a note of the wire colours from the unit and matched them up with the bikes wiring.

 

From this diagram and spare cable an adapter loom was made up to go from the unit to the bike. Connectors crimped, soldered and then heat shrinked

 

With the loom made the multiplug on the rear of the new unit was further weatherproofed with heatshrink and loom tape.

 

the new loom was fed round the headstock, along the spine of the frame and connected to the dash and gear indicator multiplugs on the bike. The clock part of the speedo worked as it powered from the permanent live (Red wire) to the unit.

 

Now to tidy the wires a bit and fit the speedo sensor and associated magnets to the front wheel and forks

The speed sensor consists of a fixed static sensor and 2 small magnets mounted to a rotating surface, in this case the front disc. When a magnet passes the sensor head an output (square wave positive or negative voltage, if you are interested) from the sensor is created via it’s internal electronics, this output is of a constant amplitude, the only thing to change is it’s output frequency which will vary according to the number of times a magnet passes it. This output is be fed to the gauge electronics and together with a known circumference of the front wheel will give a speed indication. This is a Hall effect sensor, used in Anti-Lock Braking Systems (ABS) systems.

To mount the sensor I used a small scrap bit of sheet steel cut, smoothed and drilled to accept the sensor and the bottom caliper bolt. The sensor is full threaded with locking nuts to get the correct gap for it to work correctly. The Instruction sheet I got with this unit did not give a gap. 0.8mm – 1.5mm is a common distance for this type of sensor to give good results without a collision

 

Last thing to mount is the unit itself. I used the standard GS125 clock bracket. All that was needed was to drill 2 additional holes (5mm) for the 3 mounting points on the unit

 

The unit has 3 mounting posts moulded into the plastic base, these were tapped M4. M4 X 16mm Allen screws and washers held the unit well.

As I was using stainless steel screws in a plastic housing I applied semi permanent Loctite to the threads and nipped them up VERY carefully. With the bracket fitted to the bike via the standard mount holes it all felt solid and looked good. All wiring was then tidied up and hidden in the headlight bowl, they just fitted.

The instructions were a bit vague and in at least one case inaccurate, but enough with a bit of thinking to set up for the GS125.

First job is setting the clock -

A long press on button a (left button) will cause the hours digit to flash, then a short press of button a increments the hours. Another long press on button a with the hours flashing will now flash the minutes, (not button b as the instructions would have you do). Again a short press on button a will increment the minutes.

Set wheel circumference and change to MPH -

By pressing both button a and button b (right button) together you enter the parameter settings menu. A c1920 is shown with the first number flashing, this is the wheel circumference setting. Use button a to increment the numbers and button b to change between numbers. You can use Circumference = π x Diameter of the wheel or run a cloth tape measure round the front wheel to get the figure in mm. The next short press of button b will enable you to change from KPH to MPH.

To change from a single pulse (single cylinder 4 stroke) to any other cylinder arrangement button b from the KPH to MPH setting with take you here. I have read that if you change from the default single pulse it will NEVER go back only forward so I left this well alone on the single cylinder GS125.

The instructions for Trip reset etc. were accurate from the sheet to do these jobs. My GS125 is not fitted with a fuel level gauge so the gauge will show empty and the yellow warning light will stay on till I get suitable 10Ω resistor to go from the unused Yellow / White wire to ground. This will tell the unit I have a full tank. Luckily the water temperature light is off by default.

As a check I will mount my phone and use a GPS speedo app to fine tune the speedo setting.

Unit on and ready to go.

Edited November 15, 2020 by linuxrob

[fastbob]

Wow . I admire your determination but that's a lot of effort to go to to know what the revs are on a 125 single .

[TimR]

Have you had to have thr front wheel rebalanced with the additional weights fitted ( magnets ) ?

[strikeout]And did you set the circumference for the size of wheel or the circle that the sensor moves in

As would expect the set up to be on the rim not the hub if you have placed wheel rim dimensions ...

Time will tell if it starts reading 1000mph ..[/strikeout].

But then i suppose if it know that each revolution of magnet = the circumference then it can do the maths to calculate the speed /distance travelled so ignore the above ....

Edited November 15, 2020 by TimR

[linuxrob]

Have you had to have thr front wheel rebalanced with the additional weights fitted ( magnets ) ?

 

Cheer Tim

They are quite light and epoxied to the inner part of the disc so will not affect it.It is a GS125 and 60MPH is a fantasy on this bike.

[linuxrob]

Wow . I admire your determination but that's a lot of effort to go to to know what the revs are on a 125 single .

 

Well Bob, you know.... I need to get out more

[WD-40]

Tidy job. Small screen to protect the back of it next?

[Trooper74]

Tidy job. Small screen to protect the back of it next?

 

IP Rating .... ?

[linuxrob]

Tidy job. Small screen to protect the back of it next?

 

IP Rating .... ?

 

IP 44, splashproof!!!!

Oddly enough was thinking of that, will look on eBay for a nose fairing off a GS125 or maybe a small flyscreen.

With it's eBay, Exhaust, carb, day running lights, heated grips, camshaft and now Speedo I could paraphrase "The Vapours" and it's turning Chinese!!!

Rob B

[Trooper74]

IP 44, splashproof!!!!

Rob B

 

IP44 .... I wouldn't breath on it heavily ....

My Himma instrument binnacle is IP68 .... the worst of all ... I have to remove the cover monthly and dry it out with a hairdryer ...