Fuel Level Sender repair - Vespa PX and LML Stella scooters

I've been asked a few times on how I managed to make my Genuine Scooter Stella 2T fuel level sender reliable.  So when the opportunity to fix the sender unit on my friend's scooter came up, we decided to take photos this time.

The principle of the sender is very basic, but some of the materials chosen when it was manufactured were not ideal.  The sender works with a float on the end of a stiff wire arm.  When the float moves around the fulcrum pin, a wiper contact slides across a variable resistor.

The first step is to pry open the tabs which retain the cover over the mechanism.  It is wise not to over-bend these, because they are small and fragile.

Once the cover is removed, the mechanism is exposed.

The float goes up and down which moves a wiper contact along a nickel-chrome wire wound around an insulating material.  This forms a variable resistor.  The problem is that this insulating material is not very stiff and over time it bows away from the wiper in the middle.  When the nickel chrome wire is no longer in contact with the wiper it causes the gauge to read EMPTY.  Rather than risk snapping the small gauge nickel chrome wire and re-winding it on a different material, I have shaped pieces of non-copper-clad circuit board material into a fat "T shape" with the bottom of the "T shaped" piece 20mm wide.  The upper sides of the T are just to keep it from falling downward will be trimmed off to fit the cover back on, so I just eye them up before cutting them.  The final trim is done with a dremel cutoff tool.  If all you have is single-side copper clad board, just put the copper AWAY from the resistor.

It takes two of these to wedge the resistor back to a flat shape.  I use a file to remove some of the material of one of the T shaped pieces so they fit just right.  These aren't particularly critical, you can see I just cut them out roughly by hand using the dremel tool and didn't even bother with a straight edge.  The "T shapes" fit in from the top behind the resistor and should press down and straighten the resistor so its flat.

The resistor should be approximately 150 ohms at the empty position, and should decrease in resistance toward the full position.  If it doesn't read exactly 0 ohms when the float is all the way up, it doesn't really matter.  This one only went to 15 ohms, and worked fine when re-installed.  The video shows how we checked the operation with an analog multimeter.

Once the resistor is wedged to stay flat, the wiper stays in contact throughout the range of motion.  The cover can be replaced and the tabs gently bent back over to keep it in place.   This type of repair has lasted umpteen thousand miles.

In the body air cleaner for the Vespa Large Frame

Perhaps this problem only plagues a large frame Vespa with the LML reed block engine, but I've been fighting oil-fouling of the stock air cleaner since my engine was kitted.  The throat on the reed block is very short with little length to keep high velocity oil droplets from backing up, the stock reeds (Which don't break hundreds of miles from home like the carbon fiber ones can) have a bit of spit-back.  This spit-back oil is coalesced onto the air cleaner, which restricts air flow.  Umpteen miles down the road after cleaning the air filter, and the bike is running rich again.  My carburetor is tuned to exactly, that it can't tolerate any loss of air.  Even changing the grade of fuel is a noticeable change in performance. 

So the only solution I could think of is to move the air filter out of the stock position.  This gives two benefits.  It leaves space for a velocity stack on top of the carburetor, and also prevents any spit-back from fouling the air filter.

I've seen alternate air box covers which give more space. I've seen filter elements inside the rubber bellows.  I've seen the bellows eliminated, and a pod filter used to suck up hot engine air and dirt from the road.  None of those solutions sounded like a good idea.  I wanted an air filter in the body of the scooter.  The air entrance at the front of the seat isn't the only path for airflow, so using that area isn't guaranteed to be all filtered air.  Right where the bellows attaches to the body is the ideal place to put a filter.  The challenge is that this space is shared with the petcock rod, the oil tank, and the fuel tank.  A soft foam filter with some length and small girth could squeeze in there.

I made a 3D printed flange with a clip to attach to the opening in the body.  I selected a Honda CT90 foam air filter element and closed off one end.  There was so much foam there, that I elected to cut the Honda element in half, and still have more surface area than the stock P200 air filter that I was running.  The open end was glued to the 3D printed flange.

The inside of the body is coated in a foam material, presumably for sound deadening, so a perfect seal isn't really crucial.  It took a little bit to push the air filter foam into the hole, and get it positioned so it was open in the center.

The result is very promising.  The performance is fine for my 20/20 carb.

Vespa Smallframe SIP VAPE electronic ignition

The SIP VAPE Performance Ignition obtained from Scooter Mercato is an amazing upgrade.  No more cleaning dirty points, or points that float at high revs.  The engine starts with barely a half a kick instead of several.

The schematic looks like this now.