Gas Guage Troubles

[cywelchjr]

I'm having trouble with my gas guage on my 80 G. When it get hot out, the guage quits working. Now I figure it's gotta be one of three things, the guage, the regulator for the guage or the sending unit. Because of my background in electronics, and the fact that it doesn't seem to matter how full the tank is, and that sometimes at slightly lower temps the guage will go high I'm suspecting the regulator, but I can't figure out where it is. Can someone tell me where to look for it so I can check the voltage coming out of it when the problem occurs? I really hoping for that part, or barring that the sending unit since I have an extra sending unit. I don't really want to have to replace a good working tach, especially since it's not showing an wobble or other strange behavior like I hear they can.

Thanks in advance.

[Crazcnuk]

Well, the sender is in the tank, as you know, and I think the rest is in the speedo.

There is a module in the speedometer that sometimes goes bad.

[webbcraft2150]

There is a voltage regulator (no longer available) in the tach housing. The OEM service manual has a trouble shooting guide for checking everything. The gauge on my G also has a mind of its own so I rely on the odometer to "estimate" how much fuel I have. The regulator on mine will check good one day and bad the next so I gave up on it for the most part. Your best bet is always ride with someone on a Special and fill up when they do, that way you should never run out of gas.

[randy]

Cy,

The fuel guage regulator is mounted on the underside of the tach. It's a little black box with red, black, brown leads. The regulated voltage at the sender should be 7VDC. With your background in electronics, if it's bad, you should be able to bang up a 7V regulator out of a 7805.

[cywelchjr]

The fuel guage regulator is mounted on the underside of the tach. It's a little black box with red, black, brown leads. The regulated voltage at the sender should be 7VDC. With your background in electronics, if it's bad, you should be able to bang up a 7V regulator out of a 7805.

That was somewhat my thought based on hearing that the regulator is made of unobtainium. Either with a 7805 or the variable version (don't remember the part number off the top of my head) and a zener diode setup. Used to do a lot of that type of stuff back in the day, now I tinker on old motorcycles.

[randy]

The 317 will give you a variable (IIRC) 1.2V-40V range using only 2 resistors.

[fredintoon]

Running out of gas

Hi Cy,
there are several safeguards.
If the fuel gauge is suspect, rely on zeroing the trip odometer when you fill up.
If you forgot to zero the trip, rely on there being ~1 gallon reserve on a Standard.
If you forgot to reset the fuel taps back from reserve rely on having a cell phone and AAA membership.

[skids]

The standard models have a bi-metalic tyne (sp?) that is wrapped with a coil to heat it. The thing, over time, bends back and forth until it breaks off at its base. If this has occurred, the indicator needle will move if you tip the gage from one side to the other. I would check the sender ohms and the voltage supplied first however, because those checks are easy.

[Crazcnuk]

And if all else fails, good walking shoes...

[cywelchjr]

The guage works fine most of the time. Basically when the tach area gets hot, the guage stops working at all. I'm really thinking that it's the regulator quitting when hot. Now that I know where to look, I'll check it when it's not working and very likely engineer a replacement regulator, I may see if I can come up with a design that I can put together inexpensively and maybe see if there is any interest.