Gas gauge adjustment / repair.

[bluegrass]

Two ways I'm thinkin'.
Siphon all gas from the tank. Now pour exactly 1 qt. back in the tank (or whatever amount you'd like the edge of the red empty mark to indicate). Now your two choices. #1 remove the sending unit from the tank, and thru trial and error bend the rod holding the float, until the needle of the gauge touches the edge of the red zone. [Jus place unit back in tank after each adjustment holding it in place]. When satisfied bolt down the sending unit. If your reading is empty with that 1 qt. of gas, then bend the lever so the float would be farther from the tank top and vice versa.
#2 Or place an adjustable variable resister / trimmer pot in the sending units wire (blue with white tracer). Adjust the resister so the needle on the gas gauge reads on the edge of the red zone. Then put a tad of silicon on the adjustment screw to secure it in place. Voila ! I saw photos of this done on a m/c site years ago. Looked so simple.
Now the Big ? is--- what size variable resister. You electronic wizards out there please chime in.
BTW; If ya do the sending unit mechanical thing, while it's outa the tank, spray some carb cleaner on the units variable resister working the float lever arm to an frow to hopefully get any old gas varnish off the surface.
For my Pamplona 150, is taking exactly 1 us Gal to fill up when gauge touches the empty peg, which should leave me * 2.6 qt's as reserve.
* if it's actually a 1.66 Gal tank. ??
Whadaya think ??

[OldGuy]

I like your thinking, especially having to do with draining the tank and started with a measured amount of gas as a reference.

You may want to look at my post regarding taking the speedometer apart in the Black Cat, Rattler, Roughhouse discussion area. (The last post, at this time, was June 23 '13, so it is not too far down the list.)

I think my technique could be applied to the gas gauge needle. And your thoughts make me interested in trying.

For the gas gauge I would:
- drain the tank
- note the gauge reading
- add a known quantity of fuel
- note the gauge reading
- adjust the needle as needed

There is a bit more to it than this. Also, I notice that my fuel gauge reading goes up when I am riding, down when I am at idle. It is subtle, and a slow change, but voltage does have an affect. Therefore we would need to decide if we want to set the needle at idle of when rev'd up. I'd go for rev'd up myself.

I might play with this in the next week or so. I'll post my results if I do.

[VinylDoctor]

well if voltage is doing that.
it needs a resitor to stabilize the voltage.
it cant read correctly if the voltage keeps going up and down.

[bluegrass]

Your right on the varying voltage effecting a gauge. My old Volvo gauge used a thingy in the circuit cutting and keeping the voltage to a steady 9 volts. I don't see a transformer or resistor in the wiring schematic in the gauge wiring. Might be built into the gauge.
Holding an amateur radio license I should know this basic stuff, but the hard drive between my ears is suffering from CRS.

[Throwback7R]

You would need a voltage regulator " what your looking for " However I do not think the time is well spent on if you know the needle hits the bottom and you have 2 qts left .. just figure for that?

I know thanks to fuelly that my buddy gets 73.8 MPG and if I figure to fill up at around 75 miles I am good, I do not like to stretch it too far.

That is just me.

[PeteH]

Do what I do when my trip odo broke on my old Honda: write the last fillup mileage on the speedo glass with a grease pencil. When you get to that-plus-70 or so, it's time to fill up.

[bluegrass]

Thanks Pete, Excellent idea. The KISS rule "Keep it Simple Stupid" is usually the best way.
Being a tinkerer at heart, I just can't stand it, when "it ain't quite right".

It's Bud lite time.

[bluegrass]

Change my mind about this after finding I had to pull off lots of body panels jus to unplug the sending units wire harness plug in. Maybe accessible behind the taillight. I'll go with the "KISS" rule. When the gauge rests on the empty peg I'll know I've got at least 40 miles +.
Better yet, I'll carry 1 qt. of gas to get me to the nearest station, run a full tank to the sputter (pickup) point. Then fill to the ring + the qt. will tell how much usable gas is really in the tank.

[PeteH]

I don't know about that 40mi or so. When I ran out of gas once (yeah, didn't bother looking at the gauge on a long afternoon ride), it didn't take much more than 1g to fill it up to the lower ring again. I do _not_ know whether this 1.66g is fact or myth.

What I _should_ have done, and I suppose you could too, if you're following your original plan, is to start with a dry tank, add a quart (which might be about 20mi worth) and see where the gauge reads. Use that as your mental reserve.

[DanielPerrin]

I don't know about that 40mi or so. When I ran out of gas once (yeah, didn't bother looking at the gauge on a long afternoon ride), it didn't take much more than 1g to fill it up to the lower ring again. I do _not_ know whether this 1.66g is fact or myth.

What I _should_ have done, and I suppose you could too, if you're following your original plan, is to start with a dry tank, add a quart (which might be about 20mi worth) and see where the gauge reads. Use that as your mental reserve.

I ran out of gas once on flat ground. Fortunately it was a short push to the gas station. It took 1.311 gallons to refill to the bottom ring. I always do the math to fill up around the same number of miles, but I remembered a previous milage and did the milage math wrong.

I have never found the difference between the bottom ring and as much as I can squeeze in, but it doesn't look like it should be the difference between 1.66 and 1.311. 1.66 might be a myth, or it might be some trickery between "tank size" and "usable amount of gas".

[bluegrass]

I siphoned the tank to the bottom, put exactly (pump measured) 1 gal back in then drove around the corner to fill to the ring. Took .285 gal ='s 36.5 oz.
So there's my 1 qt. reserve when the needle hits the empty peg.
That's a long way from the claimed 1.77 gal with the .77 representing 3 qts.
The KISS rule rules again.