'82 XJ750RH Aftermarket Fuel Gauge Resistance Values

I bought a cheap aftermarket gauge setup from ebay. Tach, speedo, indicators, fuel gauge all in one. The instructions say the fuel gauge has a value of 8 ohms empty 90 ohms full. When I check the sending unit in my tank I get a reading of 30 ohms empty 300 ohms full. Does anyone have a way to cheat the gauge, or possibly know of an other sending unit that will work in a stock Seca tank? I really like the gauge setup and if it comes down to it I can live without the fuel gauge. Thats what reserve is for I guess.

 

trip meter is the real fuel gauge dash meter gauge is to look pretty and is not accurate enough to count on.

fill tank before each ride fill tank at end of ride. your choice I always fill at end of ride to be ready for next ride.
establish when your reserve needs to be turned on note miles driven that will give you an Idea how far you can ride till the next fuel stop.
your brain is the best fuel gauge

 

I have to disagree mine has always been dead on. I already keep track of mileage on trips and have no problem doing it that way. The warning light would always flash just a few miles before I had to put it on reserve and I know I have at least 50 miles after that but I never ran it out. I like the guage for short trips and around the town stuff where you're not really keeping track. It's nice to turn the key on and have an idea how far I can go before my first fuel stop. Like I said I can live without it. I was looking to see if anyone had a fix for this.

 

I go one step further- I write down date, odometer reading, litres filled, and dollar amount of every fill. I can tell you how much fuel each ride uses per month, litres per 100k, money spent on gas per year, etc., but I'm kinda weird about my mileage!

 

I used to commute from thousand islands to Philly Pa. (323 miles) twice a week on this bike. I kept track like that. I know people thought I was weird when they saw me sitting on a curb next to my Seca at the gas station crunching numbers on my little note pad.

 

Interesting. My fuel warning lamp comes on after I have to swich to reserve, and about 3 miles before I run out of useable fuel.

To make the Yamaha sending unit work with the gauge you'll need to build yourself a thing to take the sending unit signal, interpret it, and send a corresponding (but lower resistance) signal to the gauge. Arduino comes to mind. You'd need to do some programming, and put the final product into a waterproof enclosure (or pot it).

 

I've never had it apart, just one of those things that has always worked so I never messed with it. I was thinking of a simpler fix. Like changing the travel on the float, or soldering in a new "tap" to the sending unit to pick up a lower resistance value. A sending unit is only a variable resistor with a float attached so I'm sure it can be altered or replaced. I guess it's time to get my meter out and do some experimenting. My goal with this bike is to simplify the electronics.

 

nothing

 

This pic shows the sending unit (metal cover off) in the empty position. The set screw has no positive detent so I was able to adjust the relation of the float to the resistor contact to achieve my 8 ohms empty value that I wanted. This adjustment will also explain why other riders fuel lights come on at different levels. The second pic shows the resistor with the float in the full position. There is still about 1/4" of resistor winding unused. My plan is to remove some windings to lower the full reading closer to 100 ohms.

 

Adjusting the travel of the arm will not make the resitance fall into the range that your new gauge requires.
I know how the sending unit works.
You might be able to get the lower value, but getting the float to show full at 90 ohms might be tricky. I think you'll find that the range of motion required to do that is too small to be useful; your gauge will see a full tank when there's about 1/4 of a tank of fuel. Dropping that sending unit into the range you need will require winding a new resistive coil to suit. I mentioned using an Arduino, because to me that's more fun than winding a new coil by hand (and reversible, and easily adjustable without removing the sending unit from the tank (and has the potential to be a product).

 

Sticking 130 ohms in parallel on the leads may get you close as well. It'll get you 90 ohms on the 300 ohm reading empty end ya least, if you actually get 30 instead of 0 of full, it may be a bit off, but mine reads 0 on full.

Half may not be half, and the reading curve may be off as well.

 

Thanks I'm gonna experiment with that approach. The parallel resistor is a good idea. I'm not looking for exact. The sending unit does read zero if I adjust it so the contact travels all the way to the last winding. Should stay zero even with a parallel resistor.

 

130 and 300 will give you 90
130 and 30 will give you24

http://www.calculator.net/resistor-calculator.html?pnumberinputs=130,30&type=p&x=51&y=18

 

Thanks to all for the help. I've got this working good enough for me. Empty is empty and full is somewhere above 3/4. I could live without a fuel gauge but having one on there that didn't work at all would drive me nuts.

That resistor calculator is a great tool. I hate math. Thanks.

 

What resistor size did you use? Can't see the color stripes on the resistor too well.

Glad you got it working.

 

Radio shack only had 150 or 100 ohms in stock. I used 100ohms and adjusted the contact to get higher resistance out of the sending unit. It's not perfect. But close enough. I may change it once I see how this relates to actual gallons. For now my tank is dry untill after I paint it.

 

you can put resistors in series to add up ohms

if you look at the bottom of the resistor calc page it gives you wire resistance you may be able to rewrap the wound wires with different size and length to get your resistance needs.

could also be the fix for bad sender units

 

Didn't scroll down that far the first time. I used to work in an electric motor shop so one of my first thoughts was to rewind it. I still might in the future. My original goal was installing a new tach/speedo combo and I got sidetracked with this sending unit. For now I will leave it functional but not accurate. I'll most likely go back to this project when I can put fuel in the tank and sync up actual volume with the gauge reading. Playing with the gauge and sending unit on the bench will only get me so far.