Fuel gauge reads empty when bike is moving

[ianralph]

I've been attempting to get the fuel gauge to work properly on my '79 GS1000S.

See this thread for some background.
http://www.thegsresources.com/_forum/showthread.php?t=152373

As per the suggestions in that thread I've bypassed the simple voltage regulator in the fuel gauge with solid state regulators, one for each gauge (fuel and oil temp).

The fuel gauge now works very well.....provided you are not actually moving on the bike. As soon as I start to ride the bike the gauge changes to read empty.

I thought the problem may be related to the charge voltage - at idle the voltage is less than 12V, at above idle it's greater than 12V. So I tried simply revving the engine while stationary - the fuel gauge continued to read accurately - the voltage reg appears to be doing it's job.

The problem only appears when I start to ride the bike.

I wonder if the sender unit is faulty in some way so that as the fuel sloshes around in the tank the movement of the float causes the problem.

Any ideas or suggestions?

 

[Steve]

Is it when you actually start to move or just when you take it out of neutral?

There is a remote possibility that you have something connected incorrectly to the neutral light, giving you false readings.

.

 

[ianralph]

Is it when you actually start to move or just when you take it out of neutral?

There is a remote possibility that you have something connected incorrectly to the neutral light, giving you false readings.

.

Hi Steve,

Thanks for replying.

No - I have to be moving for a minute or so before the gauge reads empty (just as if the ignition switch has been turned off - the gauge takes a while to move to the empty position). Then when I pull up at traffic lights it registers correctly again....

I've checked the conntections to the gauge at both ends and there is nothing amiss as far as I can see.

 

[zacheriaj]

my bike kinda does the same thing. Only it always reads completely empty. UNTIL i get low on fuel than it starts coming up haha! very weird but i havent really looked into it. any ideas? prolly just a bad sending unit.

 

[Guest]

The sending unit might need cleaning and adjustment. The pain of it is, that it has to come out of the tank each time you adjust it. I cleaned mine and bent the slider so it would make better contact on the wound resistance wire, checking it with a meter. Unfortunately I got the slider too far toward the full mark, so it goes off scale when the tank is full and reads empty until I use a gallon of gas. I should have marked the position better before I loosened the slider nut to bend it in for better contact. I have another gasket, so I'll have to take it out again and tweak it before I paint the tank. Part of the problem may be that it's a '78 sending unit on a '80 tank. It kept dropping out before I cleaned it.

 

[ianralph]

Thanks all - I'll try cleaning the sender unit and let you know how I go.

 

[ianralph]

Yesterday I pulled out the fuel gauge sender unit. I did 2 things which have resulted in steady and accurate fuel level readings:

First I cleaned the contact between the slider and the resistance coil with some 600 grit wet and dry sand paper.

Secondly I packed out the float arm with some copper wire, to make up for wear and a somewhat tired spring, thereby applying a little extra force between the slider and the coil.

While the sender unit was out of the tank I measured ther resistance across the wires that plug into the harness under the tank and found that it varied smoothly as the float arm was moved up and down - reflected in the readings on the gauge when all was back together again.

I should have looked to the sender unit first - it would have saved me a lot of time! But that's life I guess - 20/20 hindsight is a wonderful thing....

 

[Steve]

One of the things I did to "Freebie" was to check the sending unit as I moved it from the original tank (had a hole in the side that was only sealed with paint) to a replacement tank. The contact tension was a bit sketchy, as you found yours, so I also moved things around to assure proper tension. I installed the float when I found it had smooth operation.

I had not ever started the engine, let alone ridden the bike, so I did not see the fuel gauge work before I made the adjustment. It might have been similar to yours, but I have no way of knowing, now.

.

 

[Guest]

Glad to hear it worked out for you.