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I TW americani non hanno tachimetri. However the sensor likely provides the pulse once per revolution that is the core of the rev-counter's function. That circuit opens and closes each revolution would indicate it is working properly.
 

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I TW americani non hanno tachimetri. However the sensor likely provides the pulse once per revolution that is the core of the rev-counter's function. That circuit opens and closes each revolution would indicate it is working properly.
I didn't get the purpose of that thing tho...
What happen if I do not connect it?
 

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Just a bit of a joke. The Flux Capacitor was core of a time travel machine from a Hollywood movie called "Back to the Future". Unfortunately they don't come in a size to fit a TW125 bttf-flux-capacitor.png
 

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Just a bit of a joke. The Flux Capacitor was core of a time travel machine from a Hollywood movie called "Back to the Future". Unfortunately they don't come in a size to fit a TW125 View attachment 149946
Ahhh hahahaha yeah I got now the joke, in Italian is called differently ^^

But seriously now, what's the purpose of that damn thing in the speedometer of the TW125?
 

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It reports all your travels and speeds to the federal government at the FBI and CIA. The FBI monitors everyone in the states and the CIA monitors everyone outside the national borders.
Well if that's the purpose it is failing since that's just a speedometer connected to nothing hahaha
Seriously tho seems that noone know the function of that thing, I am so curious about, but wherever I read I see no clues or infos about that thing
 

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If it is a mechanical tachometer it functions not unlike your speedometer, only it reports engine revolutions rather than tire revolutions which then becomes an analog for vehicle speed.
Basically a rotating drive feeds into the back of the tach and spins a magnet inducing eddy field in the aluminum disc. In a speedo the part referred to I believe is called the "Speed Cup".

Without a better picture can't tell if you have a more modern impulse tachometer. If so then it functions a little differently: "Two pairs of connections were required, one pair for the supply leads and the other for the pulse pick-up leads. The pulse leads were, in fact, one continuous wire with a loop (forming the primary winding of a transformer) taken around a soft iron core projecting from the rear of the tachometer casing. The advantages of this type of signal pick-up were that there was no break in the ignition wiring, so a break in the tachometer circuit would not affect the ignition; and that there is no direct electrical connection to the ignition from the tachometer circuit.

The secondary of the transformer, inside the tachometer case, was connected to a printed circuit that applied current pulses, originating from the distributor and therefore at a frequency depending on engine speed, to the indicating meter. The internal circuit was fed from the supply leads, one of which was taken to one of the vehicle's existing switched and fused circuits running back to the battery, the other to earth (ground). Of the pulse leads, one was taken to the contact breaker (CB) terminal on the ignition coil, the other to the contact breaker (side) terminal on the distributor. The previously existing CB to distributor wiring was discarded. Note, however, that modern ignition coils, the SW and CB connections are marked' -' and' +' for positive earth systems and '+' and '-' for negative earth systems"
 

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If it is a mechanical tachometer it functions not unlike your speedometer, only it reports engine revolutions rather than tire revolutions which then becomes an analog for vehicle speed.
Basically a rotating drive feeds into the back of the tach and spins a magnet inducing eddy field in the aluminum disc. In a speedo the part referred to I believe is called the "Speed Cup".

Without a better picture can't tell if you have a more modern impulse tachometer. If so then it functions a little differently: "Two pairs of connections were required, one pair for the supply leads and the other for the pulse pick-up leads. The pulse leads were, in fact, one continuous wire with a loop (forming the primary winding of a transformer) taken around a soft iron core projecting from the rear of the tachometer casing. The advantages of this type of signal pick-up were that there was no break in the ignition wiring, so a break in the tachometer circuit would not affect the ignition; and that there is no direct electrical connection to the ignition from the tachometer circuit.

The secondary of the transformer, inside the tachometer case, was connected to a printed circuit that applied current pulses, originating from the distributor and therefore at a frequency depending on engine speed, to the indicating meter. The internal circuit was fed from the supply leads, one of which was taken to one of the vehicle's existing switched and fused circuits running back to the battery, the other to earth (ground). Of the pulse leads, one was taken to the contact breaker (CB) terminal on the ignition coil, the other to the contact breaker (side) terminal on the distributor. The previously existing CB to distributor wiring was discarded. Note, however, that modern ignition coils, the SW and CB connections are marked' -' and' +' for positive earth systems and '+' and '-' for negative earth systems"
So basically that Speedometer of the TW125 I purchased (just some parts actually, it misses the frame and tires, but rest is complete with engine etc etc) noone knows what the hell it does XD
 

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That must be the speed sensor for the cruise control.
It could, like it could be a maximum speed limiter, but it is a TW125... A bike like that won't have anything like that I assume...
That's why I am so interested in knowing what the actual sheeeep is that thing
 

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The main problem with identification is that the speedo is sold as a sealed unit only, and is not meant to be opened up – so there are no schematic diagrams revealing its internals

Two questions – how sure are you that this speedo comes from a TW125 – and are there any electrical connectors from the unidentified component ?
 

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Discussion Starter #16
The main problem with identification is that the speedo is sold as a sealed unit only, and is not meant to be opened up — so there are no schematic diagrams revealing its internals

Two questions — how sure are you that this speedo comes from a TW125 — and are there any electrical connectors from the unidentified component ?
Dear Purple,

It is definetely a TW 125 since we purchased this whole block of parts from the TW125 by a guy in north Italy
We have the full steering system, full electrical system, the whole engine, rear fork, suspension, airbox, carburetor, rear plastic, rear fender

All come from the TW125

The connector under is of course the cable that goes directly into the front wheel for the speed and then there is what aappears to be (if I recall) a 6pin white connector, it is somewhat rounded on the edges, I assume 2 pins are for the light inside the speedometer since it has the small bulb, but the other 4 wires are like connected to that sensor I showed in the photo that it's triggered every revolution (we tested with a Tester which beeps anytime a circuit gets excited)
 

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So jannaruto, you definitely have a speedometer, not a tachometer.
And you were teased again about the "cruise control" or "speed sensor" , the box around object in your second photo is the speed cup and aluminum eddy current disc for the speedometer and odometer functions.

Are you just trying to understand it, or repair it?
Does it have a mechanical problem, missing pieces, or an electrical problem?
Review the Service Manual for help. Here is a downloadable copy:TW200 Service Manual - searchable pdf
 

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Discussion Starter #18
So jannaruto, you definitely have a speedometer, not a tachometer.
And you were teased again about the "cruise control" or "speed sensor" , the box around object in your second photo is the speed cup and aluminum eddy current disc for the speedometer and odometer functions.

Are you just trying to understand it, or repair it?
Does it have a mechanical problem, missing pieces, or an electrical problem?
Review the Service Manual for help. Here is a downloadable copy:TW200 Service Manual - searchable pdf
I am just trying to understand what it is and what it does for the bike since it seems to do actually nothing at all

Doing nothing like: hey I am going to put 100 grams of sugar into the ocean because, yolo

That's what I feel that thing is for... Seems to have no use at all
 

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“If” its purpose is to send a single pulse every revolution, the only reason I can see for that, is at top speed, it would be able to send a signal to the rest of the bike preventing any further increase

As you have already mentioned, this is rather unlikely on a TW125, which is notoriously underpowered in the first place

Having said that (however), the TW125 has a few tricks up its sleeve that are not found on the TW200 – the carb heater being just one of them

It is entirely possible that this a “speed limiter” for a 125 in your region – the component in question would detect “top speed”, after which, presumably it would “restrict” the bike somehow from going any faster ……
 

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Discussion Starter #20
“If” its purpose is to send a single pulse every revolution, the only reason I can see for that, is at top speed, it would be able to send a signal to the rest of the bike preventing any further increase

As you have already mentioned, this is rather unlikely on a TW125, which is notoriously underpowered in the first place

Having said that (however), the TW125 has a few tricks up its sleeve that are not found on the TW200 – the carb heater being just one of them

It is entirely possible that this a “speed limiter” for a 125 in your region – the component in question would detect “top speed”, after which, presumably it would “restrict” the bike somehow from going any faster ……
Well so maybe it is that I assume...
 
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