Fuel gauge adjustment?

[CaptonZap]

Nothing worse than having a fuel gauge that isn't even close to accurate, is there?
I measured the resistance of the sending unit, 79F, and it was within specs.
When in use, and full, the gauge reads just above half. When the wires going to the gauge from the sender are shorted, 0 ohms, the gauge reads around full.
So the question is, is there a "zero" adjust on the gauge, if one were to take the gauge case apart?
Or would I be better off to parallel a resister with the sending unit, such that it read correctly at near empty?
CZ

[natemoen]

If the sender tests good then maybe all it needs is the float rod bent so it reads right.

[crazy steve]

...So the question is, is there a "zero" adjust on the gauge, if one were to take the gauge case apart?
Or would I be better off to parallel a resister with the sending unit, such that it read correctly at near empty?
CZ

You would need two 'zero' adjustments on the gauge to accurately set it; one for the 'low' reading and one for the high. A single adjustment would only allow moving the range either up or down, so you would only be right at full or empty. Trying a resistor at the sender would do the same thing, although you'd have to install it in series (not parallel) or the gauge would read full all of the time. This would make it read less full, not what you want.

Nate's idea is best; try adjusting the float arm. That may not do it, but is probably your best/easiest hope. Mine has never been accurate, offering an approximation at best. Mine showed 'full' good, but indicated empty at about 1/3 tank.

[motoman]

Nothing worse than having a fuel gauge that isn't even close to accurate, is there?
I measured the resistance of the sending unit, 79F, and it was within specs.
When in use, and full, the gauge reads just above half. When the wires going to the gauge from the sender are shorted, 0 ohms, the gauge reads around full.
So the question is, is there a "zero" adjust on the gauge, if one were to take the gauge case apart?
Or would I be better off to parallel a resister with the sending unit, such that it read correctly at near empty?
CZ

Can be adjusted taking the instrument cluster apart.......not reccomended. What I've done on mine several years ago was put an exact half a tank of fuel in, then with tank tipped up removed the sending unit and slightly bent the float arm as Nate stated, put back in tank and installed. Made the adjustment using half a tank of fuel till gauge sat on the halfway mark. Seemed to work fairly close as it will run out of fuel one needle width above empty mark and have to flip to reserve. When its full of fuel it registers above the full for some 50+miles, but having 6.5gal. initially, that end of the spectrum doesn't really matter. Just wanted it to be closer from the halfway point on down. Occassionaly it'll show a quarter tank and start stuttering and have to flip to reserve, but that's rare. Gotten used to it, and knowing at a half tank showing gives me a good idea how safely far the other 3gal. will carry me, if necessary.

[CaptonZap]

Thanks for the suggestions guys.
Bending the arm isn't going to do anything useful, since the ohm readings that the manual says are correct are the ones that the sending unit displays, and I need less at full, and less at empty, and I am against the stops at both ends, so the best I can do is change the bottom one, at the expense of the top one. The problem is that at full excursion of the float arm, the ohms reading is right, but it does not cause the gauge to indicate full. If I short the wires together, it will read close to full.
Today, as I was close to home, I had to go to reserve. So when I got home, I measured the ohms that the sender was reading, and got 80.
I got a 600 ohm pot, and hooked it in parallel, and trimmed it till the gauge read dead nuts empty. Measured that, and came up with 40 ohms.
Measured the pot, and came up with 78 ohms, which corresponds pretty close to the 80 ohms which would half the 80 ohms of the sender.
Good so far. At least, I would know when I was getting close to the reserve point.
But as Steve says, it will not help on both ends, and help me here Steve, it has been a long time since I figured resistance in parallel.
I have 80 ohms fixed, with 8 (full position) on the float arm. What is the resultant total?

Haw! Ya gotta love the Internet. http://http://www.1728.org/resistrs.htm

It says that I end up with 7.27 ohms, which is less than I started with at the full position, which will read a bit fuller, and I end up with what I need at the empty position, which is start of reserve at empty gauge reading. That I can live with. I suppose that with some fiddling, I could get a happy medium, but accurate at the bottom is better in my book.
Thanks guys, I appreciate the noodleing. CZ.

[James England]

As far as I remember, the float mechanism is actually adjustable. I stripped one down a while ago and noticed it. The arm with the float moves a little metal tongue up and down the coil of a variable resistor. On the one I messed about with (from an XS1100), there was a small adjustment screw which altered the position of the tongue and made it 'zero' earlier or later........

[rover]

fuel guage

I just set the trip odometer, and refill at 140 miles (79F) Be familiar with the petcocks, and you will get plenty of warning when to go onto reserve, then you can do at least 40 miles. I only tried this once. When you refill, make sure you are not on reserve.

[TomB]

Lamrics UK website for part numbers has some good photos and info for setting up the fuel sender float







.

[CaptonZap]

As far as I remember, the float mechanism is actually adjustable. I stripped one down a while ago and noticed it. The arm with the float moves a little metal tongue up and down the coil of a variable resistor. On the one I messed about with (from an XS1100), there was a small adjustment screw which altered the position of the tongue and made it 'zero' earlier or later........

I may pry this one apart, and see what is inside. You would think that it would be possible to get to 0 ohms at the end of the arm excursion. That is where the resistence wire is riveted to the feed wire.
We'll see. CZ

[ViperRon]

My guage had problems when I put it back into use but conditions were not really solid. First with the correct resisters the display guage showed correctly. Next with the guage out doing a bench check the resistance off the sender was correct at the correct positions so without gas everything appeared correct. With the sender in the tank and fuel added the guage was off so I added resisters to get it to the correct position but still found a slight differance of the display when sitting still at idle and driving down the highway. I did a final resiter change to make it display correctly at the lower part of scale while at cruse speed to where it showes empty when its actually empty and reserve a little below the 1/4 tank. It actually registers full nearly a gallon from full but it was the best compromise I could get.

[CaptonZap]

My guage had problems when I put it back into use but conditions were not really solid. First with the correct resisters the display guage showed correctly. Next with the guage out doing a bench check the resistance off the sender was correct at the correct positions so without gas everything appeared correct. With the sender in the tank and fuel added the guage was off so I added resisters to get it to the correct position but still found a slight differance of the display when sitting still at idle and driving down the highway. I did a final resiter change to make it display correctly at the lower part of scale while at cruse speed to where it showes empty when its actually empty and reserve a little below the 1/4 tank. It actually registers full nearly a gallon from full but it was the best compromise I could get.

Do you happen to remember what values of resisters, applied where, got you close?
I put an eighty two ohm across the tank leads, and got the gauge reading dead nuts empty at the point that the reserve turns on. The gauge will read below that, but that is good enough. Unfortunately, at 4 gal, in a standard tank, the gauge reads less than half.
Taking James' advice, I pulled the sender apart, and found that there was no way to use that to fix the problem. You can adjust the wiper arm up or down, but it just shifts everything up or down the scale.
Well, at least I know when it is at reserve point now, and that is the important point.
Thanks for the input, CZ

[clcorbin]

If the sender is reading correctly per the manual, then I wouldn't mess with that. The problem is elsewhere. Either the wiring is messed up and you have some leakage (high resistance shorts) or other wiring problem or the meter/fuel gauge itself is messed up.

[CaptonZap]

If the sender is reading correctly per the manual, then I wouldn't mess with that. The problem is elsewhere. Either the wiring is messed up and you have some leakage (high resistance shorts) or other wiring problem or the meter/fuel gauge itself is messed up.

According to the manual, you check the voltage from the gauge mounted voltage regulator at the tank plug, and if it is 7 volts, it's good. Mine is.
I haven't taken the gauge out , to get to the connecters at the back of the gauge, but since the voltage regulator puts out 7 volts, I am assuming that those connections are good.
The tach needle gets a little erratic now and then, so someday in the future I may have to pry the gauge open and lube things, and that will be a good time to look at the internal 'werkins' of the fuel gauge.
I may play with the supply voltage, when the weather warms up, and see what sort of anomalies I can induce.
Till then, I know when it is getting down to reserve, and I can live with that. CZ

[skids]

With these standard model fuel gages, the tyne in the gage unit is a bimetalic strip that is wrapped with heating coils. That is what makes the needle deflect in response to the current feeding it from the variable resistor from the sending unit. The tyne can fracture and everything else will test normal, but you will get wierd fuel level readings.

[CaptonZap]

With these standard model fuel gages, the tyne in the gage unit is a bimetalic strip that is wrapped with heating coils. That is what makes the needle deflect in response to the current feeding it from the variable resistor from the sending unit. The tyne can fracture and everything else will test normal, but you will get wierd fuel level readings.

Now that, I can understand.
But it means I have to pry the gauge open, and I'm not that concerned about it, yet.
I'll store that bit of info away until the tach goes wonky, and then look into it, literally.
Thanks Skids, CZ