TPS and carburettors

[Easy-X]

Although this about my Royal Enfield, I'm guessing it might apply to a range of pre-EFI bikes.

TPS = throttle position sensor. AFAIK the minimum wiring would be a potentiometer as a voltage divider with a reference voltage on one side (usually 5V from the ECU) ground and then voltage out so 3 pins. The throttle position would therefore be somewhere between 0~5V.

Obviously a TPS is essential for EFI throttle bodies but they seem to be quite common on CV carbs. Thing is, every CDI or TCI unit that has TPS connector only has 2-pins so where's the third pin coming from? Maybe it's just frame ground but a pre-EFI Triumph with CV carbs, for example, has the third wire shared with one of trigger coil lines

The other question is: what does the TPS sensor really do? From what I read, most people sans-TPS (e.g. an old slide carb) have no problem starting and running their bikes so whatever it does it ain't much I'm thinking I could rig up a twist throttle and potentiometer on the left side in the style of the old advance/retard control on really ancient bikes. Sounds like a larf! Would it actually do much though and how the heck would I wire it given this 2-pin vs 3-pin question?

BTW no one seems to have laid hands on a late year, Indian market only, carburettor based Royal Enfield wiring diagram otherwise I'd just consult that.
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Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[Pete.]

Well actually an EFI setup will run happily in speed-density mode without TPS input but that's not a lot of cop for low speed rideability.

On a carbed bike the only purpose it can have is to optimise ignition timing according to throttle position and engine RPM where it can probably extrapolate engine load.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Easy-X]

Ah yes, that makes sense: the pulsar, ignition puckup, sensor coil... whatever name you want to call it can say something about the current RPMs but the TPS says something about "future desires"

Now I'm thinking about it, e-Throttle (throttle by wire) usually works by running a hall-effect sensor past a magnet. Same deal as a voltage divider: 5 volts in, 0~5V out depending on the proximity of the magnet. In theory a plastic throttle tube could pull a carb slide cable and have a hall-effect sensor at the same time. All it would require is drilling a tiny hole for a neodymium magnet to be glued in and getting lucky and finding an appropriate spot in the switch casing to place the sensor End result: a simulation of TPS for slide carbs!

AFAIK (i.e. brief Google search) such a combined cable and fly-by-wire system does not exist. I do like a challenge
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Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[WD Forte]

I'm sure I've discussed this before but none of you people ever pay attention
(long suffering sigh....)
My lovely lovely Majaste scooty has a tps on the carb and This 2001 scoot was a later model
just before they started using EFI
The early scoots just had a simple carb and yer basic pulser/spark unit affair

Later ones had carbs with a tps linked to a more complex Igniton box.
As they still use basic pulsers on the crank I have to assume it triggers the spark earlier in the rise of the
ignition pulse cycle to give an advancing effect.

Ignition pulses I've observed are vaguely sinusoidal if somewhat ragged and usually start with a negative pulse followed by a positive one and often some 'ringing' too
If the spark was normally triggered at a pre set threshold voltage on the positive going pulse, you would get some
kind of advance effect if you could also detect a negative pulse of certain voltage then,
if conditions are met (set by the putput voltage of the tps) use that as a trigger.

Honda used what was effectively a 6 pulser setup on the CX CDI system, 3 per cylinder
with low speed, high speed, and advance coils.
It was all a bit of a ball ache really, the Later engines with TI were much better.
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bikers smell of wee

[Easy-X]

I had an old eBike throttle in the shed so I took it apart. The rotation range is less than 90 degrees (a quarter turn) which I could live with but this particular magnet outputs based on N/S orientation. Zero degrees = low output, max turn = high output with all the variation in between. However, moving beyond the ends of the magnet (or removing the magnet entirely) returns the output to the midway.

Yeah, this seems like a lot of bother I dare say it'd be worth investigating for something like an NSR125 where ppl try and rinse every ounce of power from the thing but my Royal Enfield is more suited to doing laps at a steam rally
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Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter