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Shadow VT700c 1986, ST1300 08
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Discussion Starter · #1 ·
After dealing with the neutral and OD sensors I decided that I better deal with the annoying flickering fuel light.

Removed the fuel sensor and found out that the problem is with the thermistor that stopped working properly.
Normally it will be 1k ohm resistance but is now showing 1.35k ohm.
While a new sensor will cost north of $20 a new thermistor will be £1.75/$2.45 per pack of 5.
Having done the worst bit, removing the thermistor with little damage to the casing I'll be going for the challenge of repairing it.

I couldn't find anything about fitting a proper level sensor and gauge so for now will leave that alone...
It won't be impossible to fit 2 or 3 sensors identical to the existing but at different levels in the main tank with dedicated LED's and have it working that way.
The way the thermistor work, if anyone is curious about it, is, while submerse in petrol (gas for you guys) the thermistor will cooldown and the resistance will be the 1k ohm maintaining the light off.
As fuel level decreases the thermistor will be above the fuel level. At this point the resistance will decrease turning the light on.
The connection is quite basic. the + wire will connect from the ignition to the light. From the light will go to one of the thermistor wires, the other wire from the thermistor closes the circuit with the ground (-)
If anyone will be interested in the wiring diagram for this just let me know.

Because I have changed the halogen bulbs with LED's I'm not sure the 1k ohm will work so I've ordered 2k and 3k ones. :cool:

Pics and updates to follow
 

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I would be interested :)... mine is not working since I got the bike. Strange is that the initial point when you turn the start key, it is suppose to check if the sensor works, 5 secs the light goes on then turns off. But anyway if I go low on fuel this light never turns out (I check it at least 2 times I got to wallk the bike some miles :) good for my legs)
As I read this sensors measures temperature, when the sensor is in contact with the fuel temperature goes down, when no fuel, temperature goes up and the light turns on... but not in my case.

I recall this light goes on or little on when the bike is over 6000 rpm, but dont know why maybe electrical noise...
 

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1983 Honda vt750 Shadow
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The early bikes had a bulb check relay to test the dash bulbs.
Here is the 1986 circuit.
 

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The early bikes had a bulb check relay to test the dash bulbs.
Here is the 1986 circuit.
Ahhhh you always near my Switfy Guru, thanks, I had the diagram... bulb goes to the Indicator Light Checker and then the Fuel Sensor... so my light bulbs are OK and my Fuel Sensor is bad (cant get a new one here)
I learn to ride with counting kms, no problem. Strange is the light turns a little on over 6000 rpm, like some "discharge" or "extra energy loose" ends up in this light bulb (or Indicator Light Checker)

Sorry Husoi, dont mind my problem its Husoi's post :)
 

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1983 Honda vt750 Shadow
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If you disconnect the wires from the fuel sensor, does the light still act up at 6000 RPM?
May give you a direction to follow.
Some one here had a way to replace the themo sensor with a different part and it worked.
A little different size if I remember but it worked OK.
Maybe from a car fuel sensor. They look the same.
 

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Shadow VT700c 1986, ST1300 08
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Discussion Starter · #6 ·
This is identical to the thermistor I've ordered
Thermistor on Ebay
They are very small.
@sebadamus I welcome any input from anybody with a valid opinion.
There is only one thing I really, really dislike. When someone says bad things about my beloved country :)
Other than that, fire away (y)
@swifty2014 the star of the north as always :cool: yes, I have the diagram and tested everything as they say in the manual.
Some wise man told me some time ago that is better check the simple things before throwing parts at it ;)
This time it is the thermistor.

Because I've ordered more than 1 I'll have a play about putting small LED's (3mm ones) and make a scale with it.
 

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@sebadamus I welcome any input from anybody with a valid opinion.
There is only one thing I really, really dislike. When someone says bad things about my beloved country :)
Other than that, fire away
If you comment that because I am from Argentina, I am not that kind of douchbag, I know here are several douchesbags (wonderful word 😝 , remember it from Family Guy cartoon serie... sarcasm and critic like no other)

When you finish your fuel sensor frankenstein contraption, please post it if it works, I would surelly try to make one here.
 

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Discussion Starter · #8 ·
If you comment that because I am from Argentina, I am not that kind of douchbag, I know here are several douchesbags (wonderful word 😝 , remember it from Family Guy cartoon serie... sarcasm and critic like no other)

When you finish your fuel sensor frankenstein contraption, please post it if it works, I would surelly try to make one here.
Well... :mad:
.For you to know mister.. I'm from Portugal not UK, I just live here 😋😋😋
I'm awful with sarcasm, don't like and don't understand it :rolleyes:
Never watched family guy or any of those cartoons so I have no idea what you're talking about :p

And yes, I'll be posting pics of it and if I can be bothered maybe I'll make a wee clip of it :cool:
 

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Discussion Starter · #9 ·
New arrival, 1k thermistor (together with 2k and 3k)

The index finger is just to give an idea of the size.
294229
 
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Discussion Starter · #10 ·
All done.
I just couldn't be bothered with making a clip but here a few pics.
294252

Used a small flat screwdriver to open the casing and remove the thermistor after removing the solder from the bottom.
294253


Finished and ready to go into place.
It is a lot cleaner than when I remove it. most of it was covered in the green stuff, I think is called verdigris very common on oxidised brass, copper etc.
294254

For those wondering where the sensor goes.
Under the front seat on the back of the secondary tank.
294255
 

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Discussion Starter · #11 ·
I've abandoned the plans to make a LED fuel level indicator.
There are other options in the market already so I won't be wasting my time reinventing the wheel.
There are 2 products that I would consider.
First one is a hydrostatic fuel indicator.
The other sounds even better as it is fitted under the tank.
It is a ultrasound sensor, apparently works based on the echo changes from the tank when is full and as level goes down.
Another options is a straight slider with inbuilt resistor, not sure how this one would fit inside a bike's tank.
 
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If yours was anything like mine, Sebadamus, the little thermistor inside that cylinder was completely dissolved. Just a little ‘pill’ left from the very centre of the thing...
 

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If yours was anything like mine, Sebadamus, the little thermistor inside that cylinder was completely dissolved. Just a little ‘pill’ left from the very centre of the thing...
I recall taking out this plug from the secondary fuel tank long time ago, and it was completely sealed, not like the one @Husoi posted. So that time I try seraching to buy a new one but there is no new one of course, so I installed the plug again and started to count kilometers not to get out of fuel.
I will try again, some stuff and see if it can be replaced by what @Husoi tried.
 

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Discussion Starter · #14 ·
I recall taking out this plug from the secondary fuel tank long time ago, and it was completely sealed, not like the one @Husoi posted. So that time I try seraching to buy a new one but there is no new one of course, so I installed the plug again and started to count kilometers not to get out of fuel.
I will try again, some stuff and see if it can be replaced by what @Husoi tried.
You can get the sensor cylinder from ebay and isn't expensive.
I've contacted a company on Alibaba website that sells ultrasonic sensors and gauges.
Once I get a reply I'll update you guys.
There is a guy in Canada selling the LSK kit for just under $100
 
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I was think along the same line. $100.00 can buy me a lot of gas even if it means a few more stops.
 

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Once I get a reply I'll update you guys.
There is a guy in Canada selling the LSK kit for just under $100
Thanks Husoi! unfortunatelly buying something from the real world from my country is a pain in the arse :-(
But keep posting your discovers, something will figure out! thanks.
 
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Discussion Starter · #18 ·
A bit if good news :cool:

Found a chap that created a 4 LED level indicator.
Got the schematics and I'm in the process of buying all the parts so I can start making it.
For those with a understanding of electronics, it uses a IC and 4 sensors (thermistor)
It will indicate 4 levels.
My plan is to create a flexible strip from the middle of the lower tank all the way up to the top. The idea is to have a red LED when the level reached 1/2 of reserve tank, a amber LED for the bottom of the main tank the 3rd LED halfway up and the last LED around 1in below he fuel cap.
The indicator will have 3 parts.
Part 1 - LED indicator
Part 2 - The main circuit (brain)
Part 3 - Sensors (inside the tank)

Wired to the ignition circuit
The cost of parts will be around £35/£50 ($48/$70)
No idea how many hours it will take to build
I'll update the thread as I progress.
 

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Discussion Starter · #19 ·
Latest news :)

all parts are in.
This evening will be starting placing all the components onto a breadboard and test to make sure it's all correct.
Then will be making the indicator. (the digital display is a power supply with voltmeter and not part if the group)
295988
 

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Discussion Starter · #20 ·
So yesterday I started the prototype for the fuel level.
I must say I was impressed how well it works.
the 4 LED's light up when the tank is full (the tank here being a little bow with water) and as the tank empties the LED's will go out.
296008

13.8V is the nominal voltage that your bike will have when running.
Next is to find a cable that will not be affected by petrol (gas in US) so I can connect the sensors and fit them in the tank.
 
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