Originally Posted by mathewst

Question remains...:
how to measure fuel level (at least reserve?) i just had tank off, tried to mesure those 4 wires, but wasnt able to get to know how does they work. Anybody did something similar? Any help?

Originally Posted by Pleiades

The fuel level sender on the Z is basically a potentiometer, one side is earthed and the other side (green wire) receives a current fed from the battery via the instrument panel. The fuel gauge in the instrument panel is effectively just a voltmeter. The number of bars shown reflects the changing voltage as the resistance in the circuit is altered by the fuel sender potentiometer. Almost all fuel gauges work in the same way, so it�s should be feasible to rig something up.

What you�d have to work out first is the range of resistances produced by the sender across the range of float positions. There is no test given (or resistances) for the fuel sender in the workshop manual, but they�d be easy to work out with a multimeter either with the fuel pump assembly removed from the tank, or by leaving it in position and filling the tank 1 litre at a time from empty. Measure between the green and black wire's terminals on the sender connector on the fuel pump assembly.

You could then try and find a gauge that works within that range which might be a bit tricky (?), or get a cheap LED or LCD voltmeter and use the displayed voltage to indicate how full the tank is. The voltmeter option would probably be the simplest and neatest way to read fuel level. They are really cheap to get on ebay (something like this) and are small enough to mount in a variety of positions. It would give you a number (the voltage) which you could calibrate against the fuel level. On a lot of them the display turns off below a minimum voltage, which would/could give you a good low fuel level warning or indication of reserve.

Not sure which way the fuel sender pot works on the Z, but more often than not fuel senders have no (or minimum) resistance when the tank�s full and resistance increases as it empties. Based on that assumption, you�d get 12-14V (depending on engine running or not) when the tank was full and it would drop to whatever voltage the pot�s resistance will allow when the tank was empty. If you wanted to have a precise/constant full reading (that didn�t vary with charging voltage) you could easily fit a cheap voltage regulator/limiter to the supply to the meter so that the maximum voltage it receives from the battery would be 12.5V at 0 resistance.

If you didn�t want a numerical display, you can also get LED bar type voltmeters that are quite small, which would make an ideal fuel gauge.

Hope this gives you some inspiration, ideas and a few things to try�

Originally Posted by mathewst

Amazing reply thanks amillion.
I do know how potentiometer basically works, i just dont get 2 wires. I tried to tap those 2 no voltage in them. (Green and black) i got dash disconnected though
If i feed 12v into green in potentiometer i would need another wire eher i can mesure output voltage, black is griund i suppose.
Red and black is voltage for fuel pump?
If i can mesure voltage i can set rest up. I programmed few arduinos, will do it that way.

Originally Posted by Pleiades

I don't think you'll get a voltage reading in either wire that goes to the sender with the dash unplugged as I think the supply to the sender comes from the dash and is earthed through the sender's potentiometer (if my memory serves me right).

You should (as you say) be able to create a new (ignition switched) 12V supply to the sender and then to earth. With the new voltmeter/gauge (or whatever you decide) sitting between the supply and the sender. Something like this...

+12V -----> gauge -----> sender -----> earth

Good luck! Keep us posted...

Originally Posted by mathewst

Understood!
Now only question remains, which wire of the dash loom is one that provides ignition switched +12v. God knows i guess. (wouldnt be wise to put +12v to either unless being sure)

Originally Posted by mathewst

voltage doesnt change.
resistence however yes.
Empty tank is 140 and Full tank 20 ohms. (greenwhite and black wires)
These are readings without bike started.

What is a problem though, when I start the bike, theres some potential messing things up and I cant read resistance well anymore. (even polarity of the multimeter changes reading) I dont get this. I should maybe try with cables directly at the tank.