Gas gauge doesn't return to full after fill up

[toonbobo]

Hey everyone,
 
The last two times I've filled up my tank and turned the key on, the fuel gauge isn't registering back to full. The first long bar is missing. I know I'm filling it up all the way as the gas is probably a half inch or less away from the metal ring. I usually ride my bike all the way down to very low - 30 miles or so on trip F. Last night was the second time in a row that I've noticed this odd behavior. After I hit the road again, the missing full bar will re-appear. I just think it's odd. Perhaps the mechanism that checks the gas level is going bad? Please chime in if you've noticed this before.
 

[wessie]

It does take the fuel gauge a while to respond to change. I have noticed if you turn the ignition on when the bike is parked on the side stand and say 2 bars shows, if you lift the bike upright the 2 bars stay lit. Get half a mile down the road and a third bar lights. I can only assume the fuel gauge is on the right side of the bike and that the ECU only polls the sensor for a reading once in a blue moon.

[martyl]

I've had the gauge go from full to half then back to full. The average mileage when the gauge goes from full to half is 100 miles. I reset my trip-1 at every fill up. That's my true gauge. Mine is pretty consistent on the whole...

[toonbobo]

I reset trip 1 every fill up as well. The long bar on the gauge usually disappears right around 90 miles, about a half tank (I fill up around 180 miles routinely). This is why I think the missing bar after fill up is strange. That's almost half a tank not being registered until I ride away. I always fill up the same way by sitting on the bike and I rock left and right a few times and try to 'top off'. Oh well, thanks for the input so far.

[keithu]

You're not getting your tank truly full if you do it while sitting on the motorcycle. Moving the bike side-to-side achieves nothing because you're still basing "fullness" on the level of fuel with the bike upright.
 
With the FJ, you'll get more fuel into the tank if you park it on the sidestand while filling. No sloshing necessary.

[toonbobo]

Interesting, I'll give the kickstand a shot on the next fill up. What I meant by rocking back and forth is leaning to either side and pulling the trigger to fill up, not just rocking and trying again at even level Still, I can see how this wouldn't fill up all the way.
 
My largest fill up has been 4.47 gallons and that's when I ran out of gas. I suppose I am missing some capacity as the full capacity is listed as 4.76 gallons.

[javashot1]

You're not getting your tank truly full if you do it while sitting on the motorcycle. Moving the bike side-to-side achieves nothing because you're still basing "fullness" on the level of fuel with the bike upright.  
With the FJ, you'll get more fuel into the tank if you park it on the sidestand while filling. No sloshing necessary.

I always pop it up on the center stand. Wouldn't that give you the max fill?

[toast]

I fill up sitting on the bike and am always able to top it off. Look in the owners manual and it says how you need to fill it. I stick the nozzle in there until it clicks, then pull back on the stupid CA rubber shroud and slowly fill until it sloshes about 1/8th inch above the metal ring. If you stop before the fuel level gets to the metal baffle thing with the hole in it then you're shorting yourself about half a gallon.
 
The funky shape of the top of the tank makes it kinda difficult. You can slowly fill for quite a while when the fuel is touching that metal piece before it displaces the extra air and tops it up.

[keithu]

I always pop it up on the center stand. Wouldn't that give you the max fill?

With many other bikes, yes. With the FJ-09, no. Max fill is best achieved on the sidestand.

[keithu]

I fill up sitting on the bike and am always able to top it off. Look in the owners manual and it says how you need to fill it.

The owners manual doesn't make any recommendations regarding filling on the sidestand vs. centerstand, although it does specifically say, "be sure that no one is sitting on the vehicle."

[2and3cylinders]

My new in July 2016 Red 2015 FJ-09 averages about 41 ~ 43 mpg on our crappy 91 octane E10 fuel and the gas gauge was fairly accurate and ran down normally until recently (at about 5,300 miles) when it started sticking on full until about 105 miles then suddenly dropping to half full where it should be approximately. This has occurred over the last 4 or so fill ups except for one when I filled up and the gauge was stuck at about half way then suddenly went to full and then did the usual stick until 105 miles thing. Weird. I've run as far as 21 miles on the blinking empty light count-down and get about 2 mpg less than the mpg indicated.
 

 

[2and3cylinders]

I always pop it up on the center stand. Wouldn't that give you the max fill?

With many other bikes, yes. With the FJ-09, no. Max fill is best achieved on the sidestand.

Really, it takes more on the side stand?  Illogical but I'll try it.  Wonder if the stuck on full until 100+ miles will cease and desist if I fill it on the side stand???

[DavidS]

Ok, I'm not an motorcycle design guy, and I may be full of sh*t, (and I'm sure someone will tell me if I am) but logic tells me that if you put it on the side stand, the tank is tilted to the left, and the opening is now lower than the right side of the tank. That tells me that you wouldn't be able to fill the right top part of the tank. If the bike is on the center stand, the opening is the high point, and you should be able to fill both sides to capacity.
 
Of course that assumes the inside tank dimensions roughly follow the shape of the outside of the tank.
 
Am I missing something obvious here? Or is my high school physics rusty?

[keithu]

I know it sounds crazy, but this has been the experience of me and many other forum members.

[wessie]

If you punch holes in the top of the filler neck (do not drill unless you remove the assembly from the tank to avoid swarf in the tank) then you will get more in the tank if the bike is upright, on the main stand.
 
If you do not do this then as soon as the fuel gets to the bottom of the filler neck the tank will not take any more fuel as air cannot escape. Drop the bike onto the side stand and some of the fuel will tip into the left half of the tank, maybe lowering the level below the filler neck, allowing more air to escape and more fuel to enter.