Fuel Gauge

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mnorment

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Oct 14, 2023
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Location
Roswell, GA
2023. Fuel gauge will not go past half full. Out of warranty. When I fill up the tank, it shows the 8 bars. But as you put the miles on it never drops below four. Ran out today and it was showing 4 bars.
ideas?

Is the sending unit integrated into the $600 pump?
 
Pump and float. There is a "Wiper" attached to the float arm and a segmented resistive plate. Could be that the arm is bent or blocked somehow or the wiper is bent/damaged. Might be worth having a look.

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If it was working and now malfunctions in this way, there is a good likelihood that something is just bent or loose (float slipping off the arm, etc.). It might be as simple as pulling the unit out and having a look. If you're handy with an ohmmeter you could check the resistance of that wiper as well. Maybe something is shorting the last half of the resistor.
 
My issue as i posted is the bike runs out of gas while showing four bars, or half full. I initially thought the issue was a bad gauge. However, after filling the tank it was clear the gauge is correct as I can only put about three gallons in the tank. So the gauge is correct. So now the issue isnt an incorrect gauge, the question now is why the pump only can pick up fuel when the tank is at least half full or more? Does the fuel pump have a pick up tube that may have come loose? anyone familiar with the setup inside the tank that could offer an explanation as to why it cannot pick up all the fuel when the tank is half full or less?
 
Sounds odd to me. I wonder if there was a different reason for the apparent "out of gas" behavior? Tank (not) venting, perhaps?
Is this failure been repeated or a one-time occurrence? No pickup tube to come loose.
 
Venting... I had not thought about venting so after reading your post I just drained my tank to see what the gauge would show- Guess what, one bar, which is probably about right. Started the bike, cranked right up. Ran it till it reached operating temperature, all fine. so it appears it might be a venting problem. I have not had the tank off, but go figure this problem did start right after i installed a fuze box under the rear seat. To do so I had to run a 14 gauge wire from the battery back to the fuse box. I did lift the tank, i mean like an inch, to get the wires under the tank but they are not being pinched. But, in do this i guess I might have "messed" with the vent tube. Thanks for the guidance.

So, couple questions on the vent tube. I assume the tube poking up inside near the gas cap hinge is the vent tube? Do you know how this system works or where the vent goes?
 
Venting... I had not thought about venting so after reading your post I just drained my tank to see what the gauge would show- Guess what, one bar, which is probably about right. Started the bike, cranked right up. Ran it till it reached operating temperature, all fine. so it appears it might be a venting problem. I have not had the tank off, but go figure this problem did start right after i installed a fuze box under the rear seat. To do so I had to run a 14 gauge wire from the battery back to the fuse box. I did lift the tank, i mean like an inch, to get the wires under the tank but they are not being pinched. But, in do this i guess I might have "messed" with the vent tube. Thanks for the guidance.

So, couple questions on the vent tube. I assume the tube poking up inside near the gas cap hinge is the vent tube? Do you know how this system works or where the vent goes?
The vent tube runs down below the bike. Sticks out the bottom. There is a retainer or two that holds it in place (but not tightly). Vent tube can easily be pulled up (or accidently kinked). #42-#45

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M, While you're working on the vent tube, re-set your trip meter whenever you fill up. Then assume 200 miles (5 gals x 40 mpg) until you need to find some gas +/- 50 miles. YMMV
 
Venting... I had not thought about venting so after reading your post I just drained my tank to see what the gauge would show- Guess what, one bar, which is probably about right. Started the bike, cranked right up. Ran it till it reached operating temperature, all fine. so it appears it might be a venting problem. I have not had the tank off, but go figure this problem did start right after i installed a fuze box under the rear seat. To do so I had to run a 14 gauge wire from the battery back to the fuse box. I did lift the tank, i mean like an inch, to get the wires under the tank but they are not being pinched. But, in do this i guess I might have "messed" with the vent tube. Thanks for the guidance.

So, couple questions on the vent tube. I assume the tube poking up inside near the gas cap hinge is the vent tube? Do you know how this system works or where the vent goes?

The long explanation.

Yes, that orange grommet is the top of the vent tube.
You will notice a small hole in the gas cap near the hinge that matches that grommet.
The tank vents through the gas cap where there is a system of check valves and out to that grommet.
The check valves in the cap can get gunked up (technical term) or corroded and fail to work properly, not likely on a new scooter.
That grommet is the top seal for a steel tube that runs through the interior of the fuel tank and exits out the bottom of the tank on the left rear.
There is also a drain tube in the 9 oclock position of the well in the top of the tank where the gas cap assembly lives to drain spilled fuel or water from that well. That drain is also a separate steel tube that runs through the interior of the fuel tank and exits on the bottom of the tank on the left rear, near the vent tube.
On early scooters there were 2 drain hoses from those tubes leading out the bottom of the scooter.
On later scooters those 2 drain hoses are "Tee'd" together with only one hose leading out the bottom of the scooter.

Pour a light liquid into the vent tube at the orange grommet and see if it drains out under the scooter. If so the vent line is not likely blocked. Blowing air through the vent line will not be a good test if there is a blockage below the "T" since air can travel back up the drain line if blocked from exiting under the scooter.

If the liquid drains out of the vent line, then it might be time to examine the gas cap.

Now aren't you sorry you asked??


PS- There is a second drain tube sticking out under the scooter that is a drain from the air box. There is a small round filter in that line.


dan

YMMV
 
PS- There is a second drain tube sticking out under the scooter that is a drain from the air box. There is a small round filter in that line.
Are you sure about this? I was not aware and I thought I was up to speed on this stuff. What Gens? Certainly not a Gen I. Or Gen II? Or..... this has to do with the California only evaporative canister system?
 
What if the float is sticking? I always reset one trip when I fill up and when I hit 300 Kms (180 miles) I look to fill up.
 
What if the float is sticking? I always reset one trip when I fill up and when I hit 300 Kms (180 miles) I look to fill up.
Post #6 and #8 established that the level sensor is working as intended.
Problem, at this point, seems to be that the engine is behaving like the tank is empty when it is not.

@mnorment , next time you have taken the bike for a ride of 25 miles or so, stop and open the gas cap. IF the issue is venting, you will hear a "Woosh" as air enters to fill the vacuum. (This should also allow you to continue if the engine seems starved for gas.) Be careful, if a tank is not venting properly, the fuel pump can create enough vacuum to partially collapse the tank.
 
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Update on the facts,
1. Fuel gauge shows full when tank is filled up, 8 bars
2. I reset a trip meter so I know how many miles I have been, I can go 275 miles easily.
3. I have driven 275 miles with the fuel gauge still showing four bars
a. this means venting is not the issue
4. I filled the tank on the way home. At home I siphoned the gas out
a. 8 bars showing and siphon 5 gal out
b. Gauge now shows 1 bar.

So, I believe the float is sticking at half tank. I suspect when I stuck the hose in to siphon the fuel
I dislodged the float. I ran the tube in towards the back of the tank near the seat assuming this would
be the lowest section of the tank, and probably when the pump and float are located.

since resetting the trip meter alleviates any issue of running out of gas I'm going to do this test
again before pulling the tank and pump out.
 
Anatomy of a gas cap...
https://www.fjrforum.com/threads/gas-cap-modification.18042/post-722219
Includes a checkvalve-ectomy and a means to remove key when cap is open. (I wouldn't do either but some decent photos on disassembly and cleaning...)

Good to see some of my past documentation is still helpful. The check valve castration was prompted by the habit of first gens (which I had then) had a habit of boiling over from the heat below the tank. I’ve never felt a need to castrate my cap for my 3rd Gen.

The removable key thing was just an observation. I never did that even on my old 1st Gen which has now moved on to a new owner.
 
Update on the facts,
1. Fuel gauge shows full when tank is filled up, 8 bars
2. I reset a trip meter so I know how many miles I have been, I can go 275 miles easily.
3. I have driven 275 miles with the fuel gauge still showing four bars
a. this means venting is not the issue
4. I filled the tank on the way home. At home I siphoned the gas out
a. 8 bars showing and siphon 5 gal out
b. Gauge now shows 1 bar.

So, I believe the float is sticking at half tank. I suspect when I stuck the hose in to siphon the fuel
I dislodged the float. I ran the tube in towards the back of the tank near the seat assuming this would
be the lowest section of the tank, and probably when the pump and float are located.

since resetting the trip meter alleviates any issue of running out of gas I'm going to do this test
again before pulling the tank and pump out.
This ->https://www.fjrowners.com/threads/h...e-little-white-tab-the-trick-revealed.159493/ looks like an extremely useful thread when the time comes for pump removal.
 
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