Adjusting Fuel Reading

The flashing bar comes on when I have a good 50 miles left until empty. It also drops a bar from full after about 35-40 miles. Being an awkward old git, I don't like this and wish to make the gauge read full for longer and indicate low fuel when it has far less than 50 miles to go- say 25.

In the old days, I would bend the sender wire down a bit, to give a 'more full' reading. But... I understand these 1300s have a duel tank. So, how does this affect things? I could just strip out the tanks and work it out, but I thought it would be a million times easier to ask you good fellows, since there's BOUND to be someone who's had the tanks to bits for some reason.

So, to bottom line my question, can I adjust the fuel reading on my tank and how?

Regards, Nick

The upper tank has a normal fuel sending unit which of course can be bent. My fuel level loses one bar from full before I even get out of the gas station so I'm really considering doing the same myself. If there is a bad side I'm sure someone here can tell us.
As for the bottom tank that is not as easy. Look in the manual but it uses a sensor and the computer to determine average fuel mileage and display what computer thinks you have left based on the way you are using the throttle and speed. I don't see anyway that you can change this very much unless you could mount the sensor higher or lower.
The manual shows a little more about the name and what that sensor does

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I believe the sensor in/for the bottom tank is active at aprox 1.3 gallons remaining. So...., depending on your prior average fuel mileage readings (which mine almost always displays about 3 mpg less than actual) you may only have about 50 miles remaining after the final one bar goes away.&nbsp;<br>Bending the float rod in the main tank may solve your quick to drop from full issue. Are you getting it FULL to begin with? I always fill up to the bottom (or just above, per the manual) of the tank neck and find the gauge is very linear when comparing aprox gallons used and miles driven.

Bottom tank is 2.2 gallons. Top is 5.5 gallons.

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I've been wanting to do this mod ( adjust fuel level sender) for a while- mine goes right from 3 bars, down to the flashing bar . I have an idea that the arm on the sender needs to be bent a bit to adjust it, and/or clean the sensor contacts. I am kinda waiting to do it until I decide to change the big fuel tube between the top and bottom tanks. I hear that the sender can be taken out without removing the tank, but I figure I'll kill two birds with one stone.....

Dave.David said:

Bottom tank is 2.2 gallons. Top is 5.5 gallons.

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That may be correct. I guess what I meant to convey was when the single flashing bar and then the "fuel remaining" number displays there is aprox 1.3 +\- gal remaining. Seems aprox 50 mile "remaining" is typical per this thread if read from the beginning, not just page 2:
https://www.st-owners.com/forums/showthread.php?157217-Miles-per-bar/page2

It's not good for fuel pump cooling to allow it the lower tank to get low, so IMO you should treat blinking as "get gas now".
As for the upper, with 5 display bars and about 5 gallons, you should expect to loose one for each gallon or aprox. 40 miles.

playfair said:

It's not good for fuel pump cooling to allow it the lower tank to get low, so IMO you should treat blinking as "get gas now".

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+1 in my opinion running the tank that low repeatedly will result in early fuel pump failure.

faithsdaddy said:

The flashing bar comes on when I have a good 50 miles left until empty. It also drops a bar from full after about 35-40 miles. Being an awkward old git, I don't like this and wish to make the gauge read full for longer and indicate low fuel when it has far less than 50 miles to go- say 25.

Regards, Nick

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I've never trusted that 'miles to go' reading. I always switch to gallons to empty. It starts at 1.2 gallons and it seems to be right on the money if you take the time to carefully fill the tank ALL the way to the tippy top.

I'll jump in with the others... why do you want to wait that long to fill up? I wouldn't trust it that low and it's not good for the fuel pump. Fill up sooner and you'll never see the flashing light.

paulcb said:

Fill up sooner and you'll never see the flashing light.

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That's how I roll. On one road trip I skipped a stop and before the next one I got the flashing light. Watched my speed the light my speed the light my speed they light... I was concerned. But got in under the wire by how much I don't know. Now a fill-up as at usually at three or two bars at the minimum.

paulcb said:

I'll jump in with the others... why do you want to wait that long to fill up? I wouldn't trust it that low and it's not good for the fuel pump. Fill up sooner and you'll never see the flashing light.

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Efficiency on long trips. Less time stopped means more miles per day. I read in other threads (but I forget where) that the fuel pump was still submerged as long as you stayed above 0.5 gallons. Mine is still fine at 50,000+ miles.

jonz said:

Efficiency on long trips. Less time stopped means more miles per day. I read in other threads (but I forget where) that the fuel pump was still submerged as long as you stayed above 0.5 gallons. Mine is still fine at 50,000+ miles.

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Filling up 50 miles sooner might add 1 stop per day on an 800 mile day, but that's the far, far edge of the data for almost all riders, not the norm.

To clarify- I don't use the miles to go calculator. I ran it out once, to see how far I get once the last bar starts flashing (50 miles). I usually do this when I get a new vehicle, because it's a good thing to know, as it varies drastically.

My main aim here, is to have less fuel in the tank when the last bar starts flashing- perhaps only 20-25 miles.

I have a 50 miles per day commute. I fill up at 250 miles, which is once a week.

jonz said:

It starts at 1.2 gallons and it seems to be right on the money if you take the time to carefully fill the tank ALL the way to the tippy top.

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It's a sensor on the side of the lower tank unit. Doesn't matter whether you fill all the way up, even carefully to the tippy top, half way up or just put 2 gallons into a completely dry tank. Once the sensor is uncovered you have 1.2 gallons left. No difference where you started, you have 1.2 gallons left.

The miles to empty has always been pretty accurate for me.... except once. Dang nab it!

paulcb said:

I'll jump in with the others... why do you want to wait that long to fill up? I wouldn't trust it that low and it's not good for the fuel pump. Fill up sooner and you'll never see the flashing light.

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Mine started flashing and I ran it 30 miles that way till I found a gas station, sweating bullets all the way. Took five gallons to fill.

Usually I fill up no more than half a tank indicated.

Lousy computer junk! Its tech idiots who are impressed by this crap that are responsible for them putting this trash on an otherwise beautiful bike.

Trump said:

Mine started flashing and I ran it 30 miles that way till I found a gas station, sweating bullets all the way. Took five gallons to fill.
...
Lousy computer junk! Its tech idiots who are impressed by this crap that are responsible for them putting this trash on an otherwise beautiful bike.

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There's a reason your bike went to flashing only five gallons down. I could point you in the direction of a tech idiot who could tell you exactly what it is, but you might end up severely disappointed when he tells you it isn't the computer.

--Mark

faithsdaddy said:

My main aim here, is to have less fuel in the tank when the last bar starts flashing- perhaps only 20-25 miles.

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If you're bent on doing this, you'll need to remove the fuel pump assembly from the lower tank and relocate the thermistor to a lower point on the fuel pump bracket. You may need to drill and tap a couple of holes and splice in additional wire, because I don't think what's there is long enough to move it very far. These parts spend most of their lives submerged in gasoline, so make sure any modifications you make are done with that in mind.

This change will render the estimate remaining range display completely inaccurate since it's based on there being about 5 liters left in the tank when the thermistor goes dry. You'll probably want to point his out to the next owner when you sell the bike or they could end up out of gas somewhere.

--Mark

Blrfl said:

There's a reason your bike went to flashing only five gallons down. I could point you in the direction of a tech idiot who could tell you exactly what it is, but you might end up severely disappointed when he tells you it isn't the computer.

--Mark

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You seem to know. What is it? Inquiring minds want to know.

(Sorry; wasn't dragging my feet on this. I left it open in a browser on a computer I don't use much and just got back to it.)

Trump said:

You seem to know. What is it? Inquiring minds want to know.

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Five gallons is about [-]what's left[/-] the amount you've consumed when the sender in the upper tank hits bottom and the gauge shows two bars. The second bar stays on until you've consumed the last of the gas in the upper tank, what's in the joint hose and enough of the lower tank for the thermistor on the fuel pump assembly to be exposed to air. Then you go to one bar.

Either the thermistor on your bike has had it or there's a problem with the wiring or one of the connectors between it and the ECM. The checks for the wiring and source voltage are in the service manual. At 75°F, you should see about 1.5 KΩ of resistance across it.

I'll wait here for your next rant about what a bunch of junk it is 'cause I'm a helpful tech idiot.

--Mark