Incorrect Fuel Gauge Reading?

[Guest]

So I had my carbs off this morning to replace the main jets. Finished up with that, replaced the carbs, tank, hoses, etc. as normal. After I filled her up with gas though, the fuel gauge reads only 75% full. The tank is definitely full. I checked the connections and they all seem solid as well. Anyone know what might cause this?

[tkent02]

Rust in the sender or corrosion in the connections to it probably.

[Frank Z.]

I've just been studying up on the same, and you may find this helpful as well.

http://members.dslextreme.com/users/bikecliff/images/GSfuelguagesendunitrepair_by_mr_jethro.pdf

Good luck!

[chuck hahn]

If the gauge reads low you bend the float arm down..if it reads too high..then bend it up. Same principals as setting the old style float in a toilet tank.
But, you need a mark to set things up to..and the only "for sure" mark on the gauge is the half full line.

So what I do is to find out the tank capacity per the manual first. If its a 5 gallon tank, then I pump 2.5 gallons at the pump. Put that in and turn on the key and let it sit a few minutes to really get a good reading..have the bike on the center stand also.

If it reads right at the half mark..no adjustment. If its off, drain the tank back into the can, remove the float and tweek the arm. Repeat till the reading is as close to the half full mark as you can get it and be happy. Now the sending unit is calibrated to the reading on gauge.

[tkent02]

If the gauge reads low you bend the float arm down..if it reads too high..then bend it up. Same principals as setting the old style float in a toilet tank.
But, you need a mark to set things up to..and the only "for sure" mark on the gauge is the half full line.

So what I do is to find out the tank capacity per the manual first. If its a 5 gallon tank, then I pump 2.5 gallons at the pump. Put that in and turn on the key and let it sit a few minutes to really get a good reading..have the bike on the center stand also.

If it reads right at the half mark..no adjustment. If its off, drain the tank back into the can, remove the float and tweek the arm. Repeat till the reading is as close to the half full mark as you can get it and be happy. Now the sending unit is calibrated to the reading on gauge.

Best to get rid of the rust and corrosion before recalibrating it, don't you think?

[OldVet66]

I haven't seen any of the gauges that have been very accurate. It is not necessarily a bad thing depending on how it acts and what bike it's on. I have an '80 tank on my '78 with a petcock without a reserve. My gauge reads full when it's full but goes to half very quickly. It is consistent though, when it says it is empty, I have between 3/4 to one gal. of gas left depending on how I drive. That's my reserve.

[chuck hahn]

Tom...eah..clean it when you take the sending unit out after the first test run...Ive never had one that was reasonably close enough for my liking anyway. Seems to me they are all off by a good margin regardless.

[tkent02]

I had one that was absolutely perfect. Full tank read exactly full, it hit reserve right at the red, it ran out of gas the moment it read empty.

Probably a fluke.

[chuck hahn]

Maybe..maybe not. all I am saying is that I like them to read as close as possible and the only known mark to register to is the half full mark. So I tweek them to where they are right on and reliable. Youll also note that on a cooler days, the bimetal strip looses heat from air rushing thru the gauges while riding and it will read low also...even after adjusting.

Stay still for a minute and it reads a bit fuller..take off and it drops off some again.

[tkent02]

Only one thing for sure, when it quits you're out of gas.

[chuck hahn]

LOL..Yup. E stands for ENOUGH riding!! Its 70s technology and it is what it is.

[tkent02]

Cheap 70s technology, and it's old now too!

[Steve]

But, you need a mark to set things up to..and the only "for sure" mark on the gauge is the half full line.

Actually, there are several "for sure" marks on the gauge.

The lines I see on my gauges are "F", "half", "red line" and "E".

Personally, knowing that the gauge reading is not quite directly related to the actual level in the tank, I choose to make my calibration point the beginning of the red line, which will happen as I need to switch to REServe. I don't care if the gauge stays on the "F" for a hundred miles, then drops like a rock, as long as when it approaches the red line, I KNOW that I will soon need to reach for the petcock.

.

[chuck hahn]

but when you fill it up to about an inch below the filler neck it goes way over the "F" line..least mine do. Thats why i suggested to use the half full line...its a known spot and known quantity of fuel. You have 2 constants that will give the most accurate reading in my opinion.

[tkent02]

There is actually a procedure someplace to calibrate all three points.