fuel guage adjustment?

[GARTHXS]

Is there any way to adjust the fuel guage on a 79f mine is not reading full when I fill it

[thewiz]

Bend the arm ...

gotta be careful that it reads empty at the right time too though.

[Pat Kelly]

Remove the sending unit from the tank and bend the arm down (like the float in the toilet tank).
Bending it down will cause the gauge to read full sooner.

[GARTHXS]

good idea

So what kind of range should I get from a tank with a little space for fuel expansion on my 79 it is bone stock

[motoman]

Don't ride the
special, but you should be able to safety go 125. Also, if you fill the tank to exactly half its rated capacity, ride around block watching where gauge settles to, remove tank, stand on front end(if your cap seal is working properly), remove float assembly, slighty benb float arm up or down depending on which direction gauge was from half tank, re-install, ride and check accuracy to half full, readjust as necessary.
fuel gauges are just a close estimate anyways as float arm slides up and down a resister causing voltage to differ, causing gauge needle to sit wherever it does, that apply to most any tank sending unit and gauge. From that adjustment, it should be fairly close on either end. When sending unit is out, lightly clean off any rust, etc. that may be on the resister. You'll see how that works once out of tank.

[GARTHXS]

special?

My 79 is a standard F'er

[skids]

Before you take the trouble to remove the sending unit from the tank and bending it, you should make sure the mechanism in the gage is not bad. I have seen many go bad. Remove the gage. It should read zero with the key off. Tip the gage to the left and to the right. The indicator needle should not move appreciably. If it does deflect and stay when you tip it, the bimetalic thing in the gage is broken from repeated stress.

[3Phase]

Is there any way to adjust the fuel gauge on a 79f mine is not reading full when I fill it

Garth, first up: No Smoking!

Measure the voltage at the fuel tank connector before you try to adjust the float sender or the gauge needle. There should be 7 volts from the tank connector to ground -- no plus/minus -- seven volts. It's supposed to be regulated and it should work all the time the key is on. If it's not 7 volts or it's intermittant the regulator is bad or a wire broken. Fix the wire or get another regulator and keep a wary eye on the odometer between fill-ups. S.O.P. for most bikes, I know, but a working fuel gauge is nice.

If you have 7 volts and the gauge is wrong the sender might be dirty and out of range or a P.O. might have 'adjusted' it by bending the float arm and the slide/resistor was shifted out of position. It can be adjusted by taking it out of the tank and cleaning and adjusting the slide on the resistor. Be careful removing the sheetmetal cover from the slide/resistor and ... don't bend the float arm.

If the adjustment range on the sender isn't enough or you get non-linear (the gauge needle doesn't 'track' the movement of the float) or the needle doesn't come up to just below 'E' with an empty tank and just at or above 'F' with a full tank you can adjust the needle offset in the gauge. You do have to open up the tachometer to get at the adjusters but the needle can be adjusted to change both the offset (needle position at 'E' and 'F') and the rate at which it moves.

It's really not as difficult to clean and adjust everything as it is to read and write about it. You can turn the key on and carefully move the sender with your hand and watch the needle the move to get it dialed in or you can check the sender with an ohm meter. The resistance doesn't have to be exact but it does have to be really close to the specs so I put the resistance values for the sender on my electrical schematic.

Have fun!


Regards,

Scott

[boyat68]

One thing for sure is that you don't use the fuel gauge as the final arbiter of your fuel situation. It is only a reference that you have fuel in the tank. You use the trip odometer and the reserve function to get you out of a sticky situation. Of course it would be nice if you could count on it to give an accurate account of your fuel on board.

[Science Guy]

Voltage

I have a simlar problem with my 79 F. I believe mine has a faulty regulator from voltage test. However I have not been able to locate a replacement regulator. What is the voltage level supposed to be regulated to? 7 volts or another value? Where can I locate another regulator? Yamaha dealers say discontinued.

[bikerphil]

There's a fuel sending unit for a Standard on eBay right now, buy it now $35. Or try member Andreas.

[red bandit]

With my standard I get 150 miles on a tank plus another 55 miles on reserve. That's getting 39 mpg.

[randy]

That's right about what I get, between 150-170 then it's reserve time. BTW, my fuel guage is very accurate, whenever I get the reserve 'bog' I glance at the guage and it's right there at "E". Maybe i'm lucky or maybe it's because my tach is only 2 yrs old?

[foreda]

Tank guage

If I remember correctly, when you hit Empty, you should have about a gallon and one half reserve.

[randy]

To help avoid confusion, "EMPTY" is on the guage, which we have determined is different on every bike.... "RESERVE" is a more accurate way to compare. The fuel capacity numbers from the Cycle '78 and '79 reviews are:

Standard - Fuel capacity, main/reserve 4.2 gal./1 gal.)


Special - Fuel capacity, main/reserve 12.5 liters/2.5 liters (3.3 gal./O.66 gal.)

Both are slightly less than what Yamaha published, but close enough. Yamaha didn't publish the reserve capacity, at least not that I can find, they only published the total:

Standard - Fuel capacity 5.3 gal.

Special - Fuel capacity 4.0 gal.

Finally, even though my guage is accurate, I NEVER switch to reserve until the engine tells me to!