Recalibrate Your ST1100 Fuel Gauge

Contributed by:

John Parker

Reseda, California, USA

To make the light come on at a more reasonable amount of fuel remaining:

1. Drain the tank.
2. Disconnect the wires to the fuel pump and warning light (top of tank) and
the wire to the sender (left side of tank about 1/2 way down).
3. Disconnect fuel cap breather hose, fuel line at the filter.
4. Remove the four bolts holding the tank in from the top.
5. Lift out the tank by sliding toward the rear while lifting (if you have
trouble, loosen the air cleaner, but we removed the tank on both of our, 93 &
94, STs without doing this )
6. With the tank out of the bike you can remove both the fuel pump and light
sensor from the top, and the fuel gauge sender from the left side.
7. Actually, you can remove the warning light sensor without pulling the tank,
but you must pull the tank to get at the fuel gauge sender on the side. The
STock fuel gauge on our STs was very inaccurate from the factory. The gauge
stayed on full, without moving for 100 miles. It then descended fairly
linearly until it touched the bottom peg on the gauge where it still had about
50 miles before actually being empty of fuel.
8. To change the low fuel sensor so that it comes on with .8 gal remaining
(instead of STock 1.4 gal), remove the small philips screw holding the sensor
to the fuel pump mounting bracket. Drill a small hole, the same diameter as
the STock mounting hole, 1/2" farther down the mount than the STock hole. Then
remount the sensor at this new location, and your low fuel light will now
indicate when you have 30-40 miles left (in our case....YMMV ;-}

Now the real reason to go to all of this trouble in the first
adjust the gauge sender so that you fuel gauge more accurately represents what
fuel is actually in the tank:

10. When you remove the sender from the left side of the tank, you will see a
float on the end of a long piece of bent metal rod.
11. The idea is to "adjust" this rod so that the float will travel the full
distance from the top of the tank to the bottom. In our case, the STock float
stopped before touching the top or the bottom of the tank.
12. There are limit tangs on the sender itself that keep the rod from
traveling the full distance necessary top to bottom of the tank.
13. By bending the tangs and the rod you will be able to fine tune the sender
so the gauge will indicate, in a linear fashion, the true level of the fuel
tank while the fuel is between the top and the bottom of the tank.
14. Here's the "catch" will see when you have the tank out, that it is
not linear in shape from top to bottom. IOW, there is no way to get the gauge
sender to travel up into the "top stack" area or the "sump" area on the bottom
of the tank. So your gauge will still rest on the top peg until the fuel drops
to the bottom of the "top stack" where the sender float can read it (.85 gal or
appx 30 miles in our case). Also when the fuel reaches the bottom of the tank,
and the float bottoms out, the gauge will rest on the bottom peg and there is
still .8 gal of fuel in the sump (where the fuel pump lives). I've never run
totally out of fuel (I've added 7.5 gal at the "pump" on 1 or 2 instances 8>0 ,
but I filled the tank after this mod using a graduated beaker. Here are the
results of my measurements as I added fuel to the TOTALLY DRY tank with the
"modified" gauge and light:

.8 gal........ gauge on bottom peg...light first on steady
1.5 gal...... gauge on red mark...light first starts to flicker
2.0 gal ......gauge at bottom white mark
6.4 gal ......gauge at top white mark
6.9 gal ......gauge on top peg
7.5 gal.......fuel at bottom of fill tube
7.75 gal.....fuel at very top of fill tube (my tube is modified to allow easily
doing this if I desire)

I have done over 40,000 miles on my bike since I did this mod and have had no problems with the gauge or sender due to its wider range of travel, YMMV of course. Also, this mod requires handling flammable liquid and carelessness could result in you and your beloved ST catching fire. If you are uncomfortable with this fugedda 'bout it