How to fix a fuel gauge

Repair Vespa PX200 fuel gauge

Howto to repair the fuel gauge of a Vespa PX200

Hello, I will try to write my first manual today because I solved my problem and took photos. Hope my search worked and there really aren't any instructions yet

Description of the problem: The fuel gauge does not work or only occasionally shows a brief reading when the tank is full.

Vespa: PX200E Lusso

It was the case with me from the time I bought it until about a month ago, since then it has not been a problem.

Action:

After you have ensured that the cables are in order and the connection of the plug in the upper part of the handlebar fits, only the fuel sensor itself remains as a source of error (all cable connections cleaned with a brass brush, etc.!). This is a prerequisite for moving on. We'll see later whether the fuel sender needs to be replaced.

This fuel gauge is located behind the tank cap under the seat, hidden under a plastic hood, which you can easily lift with a screwdriver, for example.

It looks something like this:

To get to the tank sensor and the cable connections for testing, you have to open the inner part by turning it counterclockwise. The raised edge is intended for this.

If you don't have a suitable tool to grab and turn on, you can do that with a pipe wrench (grab one of these noses and turn it), possibly also work with a hammer and screwdriver in this direction. The whole thing should be done without sparks

When everything is in the right position

you can lift the fuel sensor and at least touch the cables to measure.
If you raise it far enough, you can see which cables go to the measuring resistor, this should then be measured with the cables disconnected and be in the kilo-ohm range (unfortunately, I no longer know the exact measured value).

If this is the case, the fuel sender should be OK and you can reconnect the cables.
If you cannot see which cables run to the measuring resistor, do the following step first, then repeat the previous steps.
If this is not the case, you should change it or, if you have electrical knowledge, check more precisely what it is. Possibly he can still be saved with it.
Removing the fuel sender is a tricky business and takes a little patience.
I guess I didn't take any pictures because I was so upset
Pull up, a little in one direction, a little in the other ... You should look out for the swimmer, it looks like this:


This white part ...
In no case bend!
As soon as you have fumbled out the upper, thicker part of the fuel gauge, this swimmer first bumps into it and doesn't want to get out, continue fumbling at an angle
Done, you've got it out and in your hand

You can try the following if you look at it from the plastic side:
You switch on the ignition and carefully lift the float upwards by hand. Now the fuel sender should actually be showing something.
If not, push the fuel sender a little in all directions and see if something is happening on the fuel gauge.
You can also take a look at whether the sensing spring, which should move on the measuring resistor (this wound wire) when the float changes, is also in contact and everything is OK.

If everything is OK, slightly corroded contacts can be the problem with this measuring mechanism. First, however, check the contacts of the cables again, possibly bend the terminals a little (!) With a pair of pliers.
No improvement? Go on
Looking from behind you can see the plastic nose on the left and the hook on the right.
With pliers you have to bend the metal part to the left of the nose up or down, the main thing is at least 90 °.
With a screwdriver or pliers you can now push the left hook outwards and thus push the left plastic part down a bit. Now to the right and the hook goes out and you can separate the two parts from each other.

You can now see the measuring resistor in full glory and the scanning spring.
In the picture there are also the slightly corroded areas on the copper scanner (?).

If no damage can be seen on the measuring resistor, the following areas should be worked on with a small screwdriver or a small fine file or something similar:

Just be careful when working on the head of the spring!

Also work on the two contact surfaces behind the spring. These have contact at a third of the float position and can be bent a little towards each other to create more contact. You turn on the reserve warning light.

Make sure that the surfaces shine again afterwards, then contact should be possible.

You can gently bend the spring upwards to create a little more friction on the wire. The same applies to the protruding contact plate on the right-hand side, which makes contact with the pivot point marked in the middle.

The principle corresponds to the simple potentiometer with the contact spring as a wiper.

The fuel sender can now be put back together before you bend the left nose back into the starting position and thus close the housing again, but you should still check whether the fuel gauge shows a change when the power supply is correct when you move the float. If this is not the case, unfortunately I could not help you to solve your problem

If that's the case then

Put everything backwards and be good

aaaaber sometimes half-long, the installation was not as easy as expected, maybe I shouldn't tell you that anymore here

Well, let's start, you put the swimmer back in and yes ... in which direction again? I can't say for sure whether my tank is full of other things or whether that's normal, but it was definitely not installed as it was before I heard it ...

After quite a long trial and error, this was probably the only possible installation position:


Yes, that's the same picture as at the beginning, but when I took it out I didn't take any, they are both from the installation
The stupid thing is, if you don't want to use brute force, you can only get the swimmer into this position by lifting it up to the top of the tank and turning it.
But I didn't bring it there with my bare hand, I had to use an aid, that was a thin aluminum rod that I bent up a bit at the end.
So in, with the rod, in with the float, lift it and turn it over this curved tube.

If there is a simpler solution for this, bring it on

You should now move the float and, if possible, bring it into its final installation position. Now move it up and down and see that it can move freely, that was not the case with me in the final installation position! Now remember this position and put on the float as shown at the beginning and turn it clockwise to the noted position. This should be firm enough not to slip, otherwise you can still bend the lugs of the outer ring down a little with force.

The fuel gauge should now actually work again

You can make sure of this by tilting the Vespa to the side with the ignition on, the fuel gauge should change a little. Works best with a medium tank of fuel.

Hope I wrote that in an understandable way and the effort was not in vain

Maybe it'll help someone

You can keep spelling mistakes, I'll keep the beer

Regards Hoiss

Details

Applies to the following Vespa models:
Vespa PX200