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Old 07-08-2010, 03:17 AM
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Olsen_XS Olsen_XS is offline
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Location: Halden, NORWAY
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Fuel gauge voltage regulator....calling electronic guru's

The fuel gauge has quit. Have determined it to be the V reg. at the underside of tach (black box filled with epoxy resin or whatever). It gives no volt out, but gets about 11 V in (key turn on, engine not running). I plan to make a new regulator by using a LM317T or similar. The Q is: Do you need a resistor in the circuit to limit the current when tank is full and hence the resistance in the fuel level sender is close to 0 ohm? Otherwise I would expect to short-circuit the whole thing....?

What is the current flow in the circuit when the tank is full?

Is there a circuit drawing of this arrangement available?


1978 XS1100E, Marshall 4-1, otherwise stock
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Old 07-08-2010, 04:09 AM
randy randy is offline
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All we know about it is that it's supposed to deliver 7 volts to the tank float connector. But you probably already knew that
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Old 07-08-2010, 04:28 AM
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Olsen_XS Olsen_XS is offline
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Location: Halden, NORWAY
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Even 7 V would give a LARGE current if the resistance is close to 0 ohm...?

Or is a resistance within the gauge (needle) limiting it?

....don't like to find out what happens if the flashover occurs within the gas tank.......

....should probably forget the whole thing and spend the time on other things (read: the 2nd gear fix.....)


1978 XS1100E, Marshall 4-1, otherwise stock
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Old 07-08-2010, 12:08 PM
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cywelchjr cywelchjr is offline
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The fuel gauge system is a pretty standard system for the time frame. The gauge is a resistor itself, with a bi-metal bar that moves the needle, I'm pretty sure that the minimum resistance (which is the gauge itself) is high enough to keep current flow pretty low. I'm planning on building one as well since mine has quit, I just have gotten a round tuit . It's one of those things that while annoying, is not a real problem since I know when it's getting low by the number of miles I've gone anyways. I figure that unless the engineers who designed things were idiots, it was designed without need current limiting, that would be a bit silly in this type of gauge.

1980 XS1100G (Brutus) w/81H Engine
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Vetter Windjammer IV
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OEM Luggage Rack
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Old 07-09-2010, 05:33 AM
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Lamric Lamric is offline
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Fuel gauge info from the XS1100 Manual....

XS1100 LG "Mr T", SG "ICBM" & FJ1200
Check out the XS Part Number Finder

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Old 07-10-2010, 12:11 PM
crazy steve crazy steve is offline
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The 'voltage regulator' is a common feature on vehicle gauge circuits, and is supposed to eliminate any fluctuations in the supply voltage caused by variations in the charging system output. It's not a simple resistor; while Yamaha doesn't show what's inside theirs, typically these are similar to a turn signal flasher. A bi-metal strip controls a set of contacts, rapidly opening/closing to give you an 'average' output. So you might want to take a trip to a car boneyard for a replacement. Some research should turn something up that would work, as most OEM automotive gauges operate at between 5-8 volts. You'll find these usually attached to the back of the instrument cluster, and will generally be a small (1/2 x 1/2 x 1) rectangular metal box with two connections on it. It will also have what appears to be a small resistor visible; this isn't a resistor, but is actually a 'choke' to remove RF interference.

Or you could do this:


This may be easier than hunting for a used unit, parts look to be available, and the price looks to be right. You'll just have to find a chip with a 7v output...

'78E original owner
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Old 07-10-2010, 12:46 PM
cowboybob998 cowboybob998 is offline
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same problem

Dont know if this will help, Had the same problem on an old goldwing, they allso are 7v, in this case it was a louse connection.
1979 xs1100 f
142 main, 45 pilot, Jardeen crosover 4/2, no air box
floats @ 25.7

1979 xs1100 F
1978 gl 1000 goldwing
1981 gl 1100 goldwing
!986 venture royale 1300

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