Adding a gas guage ...

Hi folks,

I bought a tank from an XJ750 to put on my xj650 and I'd like to hook up a gas gauge to take advantage of the fuel sensor already present.

Anyone know how to make this work? What aftermarket gauge might read the 750 tank sensor that could be mounted on the front?

 

Is the sensor in the tank just a metal cylinder? If so, it just turns on a low fuel light when the gas gets down below the sensor itself. This type of setup will not work with a gas gauge. You'll need to find something else to adapt to your tank to make it work like a gauge (indicating gas levels).

 

My take on this problem...
http://www.xjbikes.com/Forums/viewtopic/t=13284.html

Let me know if I can be of any help.

Please, let us know how it goes.

 

I never did get around to building the led voltage-meter fuel gauge...I did do some inquiries to classicinstruments.com though and they seem to be able to build to your specs. I also just read someone's post on early '90's GM fuel gauges being the correct resistance range, just backwards. From what the guy at classic instruments said I would suspect there are gauges out there that would work forwards too.

 

Here's the post about the GM gauges.

http://xjbikes.com/Forums/viewtopic/t=16625.html

He says his works 0-90 ohms...I'm pretty sure when I metered mine it was 30-300 ohms, so you might want to double check.

 

So how does it work on the 750? is there some relay that does this on a 750?

I am not an electronics person. Give me a picture/diagram and tell me to connect part A to slot B ... I am fine. When you start talking R1, R2, R3, etc., I am as lost as y'all would be working with the New Testament in the original Greek ... Now THAT I can do ...

 

Hi

I involved with fuel monitoring equipment in the UK and the resistance of 30 - 236 ohms is an American resistance which only drives an American fuel gauge.
The European spec is 180-10 ohms which drive an European type gauge, however if you mix the specs you will have a fuel gauge which runs backward.
Just to confuse matters Yamaha have their own resistance spec of 0-90ohms.

So whether you start with a gauge or the sender make sure you get the compatible part to make the system work correctly.

The senders are easy to check using a multimeter, with the gauge just bridge the wires with a resistor of say 40ohms and see if the needle points to nearly empty ( European ) or full ( American ) or midway ( Yamaha )

 

I used a GM after market fuel gauge on my 750 Seca, but like previously mentioned, it reads backwards. Our sending units are rated at 90 ohms (tank empty) and 0 ohms (full tank) and the GM gauge is backwards, but works alright.
I have now found another gauge that has the correct resistance in the correct direction. I did a google search on a 90-0 ohms fuel gauge and found one for $25 that works perfect (or should) and I may replace my present gauge with one of them.
Another idea that I was thinking of doing, is to block off the sending unit, except for the last 1/4 of the variable resistor inside the tank, and just having an LED light to come on when the fuel is down to the last 1/4 of the tank. That way it would give you an idea where your at and time to fill up. Just an idea.

 

May I ask which one you found? I spent a fair bit of time looking and couldn't find one, not for that price anyways.

 

Hang on a sec Biff, is this a tank from a Maxim or a Seca? I'm pretty sure the Maxim only has a warning light which means that it's nothing but a float and a switch similar to the working guts of a toilet. There's no variable resistor inside the tank that would drive a fuel gauge needle.

The Secas used an LCD fuel gauge with 4 blocks (1 for each 1/4 of a tank). That one could be used to drive a needle but as others have pointed out, you need to measure the resistance from "full" to "empty" on the wires from the sender, then find an aftermarket gauge that would respond to those resistance values.

 

It is a Maxim 750 tank. So how could I wire an LED?

 

The maxim tank uses a thermistor if my theory is right, so when there is fuel around it, the light stays off, but when the fuel level is below the thermistor, it starts to heat up which changes the resistance and the light comes on. I ended up modifying a sender unit from a Buick to mount on the existing Maxim assembly and adjusted the arm for the right resistance needed to run the fuel gauge portion of my digital unit.

 

My tank is off of a 550 Maxim, which is the same sending unit at the one in my 750 Seca, I do know that much for sure. The both are rated at 90 ohms empty and 0 ohms full.
Here's where I found the gauge that will work:

http://www.bobsgauges.com/servlet/the-6 ... vel/Detail

 

To all you guys who want to use an XJ750 fuel sender with an XJ550 SECA instrument cluster, I have devised a solution.

The first picture is the schematic: the circuit is very simple: only three parts, not counting the connectors. I robbed those from an old wiring harness. The rest of the parts can be obtained from Radio Shack.

The current running through the sender is less that the stock setup so there should no worries about sparks. The pot is there to calibrate the fuel meter and because there is no voltage regulation, the reading varies very slightly from key on to running (from around 12V to 14V). I calibrated mine while running since that's when I'll mainly be looking at it.

The second picture is the built circuit. The PC board is a small section cut from larger Radio Shack PC board.

The third picture shows the finshed product. I used heat shrink tubing to seal out the weather.

 

Crud...

The pictures in my previous post are shown in the wrong order. Apparently you have to upload them last to first. Sorry about that.

 

Man, I gotta review these posts better...

One more edit: The third picture should show the completed assembly.

Here it is:

 

Any suggestion on how to use it on a 650? That was the original question as I am putting a 750 tank on the 650 (XJ Maxim, not seca). The issue being that I need an actual display unit for the signal from the tank.

 

I have the tank with a sending unit in it on my 750 Seca that came off of a 650 Maxim (that's what I was told it was from) So being it had the unit in it already, I just needed to find a gauge that worked with the ohms of the sending unit. I found the GM gauge that worked but it was backwards I just took it apart and reversed the letters, so it reads right now.
Then I found the right one that actually reads backwards. It's supposed to be 90 ohms empty and 0 ohms full. It should work perfect.

 

That was my initial problem. I have an XJ650 with an XJ750 tank and I wanted to use the fuel sender. That was the main reason I got the XJ550 SECA gauges. Plus, I liked the battery gauge, the left and right signal indicators, and the round tach and speedometer.

 

Easy access to the instrument guts is a big plus too, and there's lots of room for slight modification to fit say, a speedo that goes past 80mph.