Tach

[kflyboy]

The tachometer on my bike has the opposite problem. Tachometer works perfectly, the fuel gage quit working. Is that repairable or just replace the tachometer?

[kboehringer]

Special or Standard?

kflyboy,
It is slightly more likely that the sender unit in the tank is bad not the indicator or level gauge in the tachometer.

Have you recently had the tank off? Are you sure the connector is connected properly. The connector is at/near the back of the tank. It is a small 2-wire connector.

Do a search, someone here posted an OHM check that can be performed on the fuel level sender (Standards) or level sensor (Specials). It should be easy to verify if the unit is functioning properly.

KURT

[kflyboy]

kflyboy,
It is slightly more likely that the sender unit in the tank is bad not the indicator or level gauge in the tachometer.

Have you recently had the tank off? Are you sure the connector is connected properly. The connector is at/near the back of the tank. It is a small 2-wire connector.

Do a search, someone here posted an OHM check that can be performed on the fuel level sender (Standards) or level sensor (Specials). It should be easy to verify if the unit is functioning properly.

KURT

It's Monday' I forgot to mention that I checked the sender in the tank. It registered 28 ohms at a little less than half a tank. I will pull the tank and double check the connections or it could be a broken wire inside the harness. Thanks for the heads up. Electrical stuff is a mystery to me.

[Loch]

kflyboy

jump between the frame harness low fuel connection,(green and black) ignition on, you should get low fuel light. if not look at harness or bulb. if light goes on then its the thermistor or wiring to the thermistor.
ive bought a thermistor on line for $10.its the most likely problem.

[DiverRay]

Loch, he has a Standard with a gauge, not the Special with a low fuel light. They work differently, as the gauge uses a 7V regulator in the tach to keep the voltage to the tank down. The gas gauge can be gotten to, but you should know electronics at least a little bit in order to try and repair it. Easy start would be remove the tach from mount housing, and re-flow the solder on all the joints. That should help a lot of the time, but if not, it involves major surgery. I think there was a thread on testing the gauge at one time, but it's been a few years....

[Loch]

my test on a standard will give a full indication.

[mack]

Fuel gauge

The Haynes manual has the test for the fuel guage at empty, half and full. 3Phase posted the test last fall with the numbers but I can't find it. If Scott doesn't chime in on this, I'll grab my Haynes in the morning and give the description.

[bikerphil]

the fuel gage quit working. Is that repairable or just replace the tachometer?

I have repaired these before, not easy though. First, you would need to open the tach up without destroying it. The fuel gauge is a separate unit inside that can be removed. Usually the problem with the gauge is the bi-metal strip breaks in half. It most likely can be soldered back together, it is a delicate procedure that takes some patience. Tachs for the Standards are pretty common and available so replacing the whole unit may be a better option unless you like to tinker and repair things, GL

[DiverRay]

Per Yamaha Factory manual:
Sending unit: Full = 6 to 10 Ohms, 1/2 tank = 28.5 to 36.5 Ohm, empty = 75 to 85 Ohms.
Gauge: (Tach connector)
Brown to ground should be 12V (battery)
Green to ground should be 7V.
At the sending unit plug, Green to ground should be 7V.
This should help!

[3Phase]

Oh boy! I haven't had to work on the fuel gauge part of the system since I made a new 7V regulator and rebuilt the gauge and the sending unit.

Okay, I found the pictures....


Up in the tachometer housing is the 7 volt regulator. The current from the regulator first goes to and through a resistor wire that's wrapped around a bimetallic arm for the fuel gauge indicator needle. As more current flows through the resistor wire the arm heats up and it moves the needle from the Empty mark to the Full mark.

After the fuel gauge, the current runs through the Green wire from the tach to a variable resistor in the sending unit in the fuel tank.

From the sending unit resistor the current goes directly to ground through the Black wire.


So, what does that mean?

It means that if you have 7V on the Green wire at the fuel tank then the 7V regulator is working and there is continuity through the gauge, the tach connector, and the wiring harness.

If you don't have 7V on the Green wire at the fuel tank then it could be that the 7V regulator in the tach is bad, the resistor wire in the fuel gauge is bad, the tach connector at the harness is bad or the Green wire is broken somewhere between the tach and the tank.


If you don't have or want to use a voltmeter to see if the fuel gauge is working, use a jumper to ground the Green wire somewhere not right next to the fuel tank and watch the gauge needle. Don't keep the jumper in place for too long or you will eventually burn up the gauge but the needle should move over to and past the Full mark. If the needle doesn't move then it could be that the 7V regulator is bad, the resistor wire in the gauge is bad or the mechanical part of the gauge is broken.







.

[2manybikes]

Fuel gauge

Great thread! Thanks for everyones input, and kudos to 3PHASE for his detailed commentary. The gauge on my 79F quit a while back, and I decided I would just do without it. I know just enough to use the instructions to tear into this sometime this winter. Thanks again, this forum rocks!

[kflyboy]

tach

Great thread! Thanks for everyones input, and kudos to 3PHASE for his detailed commentary. The gauge on my 79F quit a while back, and I decided I would just do without it. I know just enough to use the instructions to tear into this sometime this winter. Thanks again, this forum rocks!

Thanks for the diagnostics and the photos. I will re-test the sender unit in the tank and then start on the wiring and testing the tach. I will let you guys know what I come up with. You guys are the best-couldn't keep the bike running without you!!