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Solex (En)


For many years a Solex moped was stored in the garden house of my parents. After my parents moved, the Solex was parked in my garage. The Solex suffered a known problem, a broken fuel pump and in the time the Solex did work it could suddenly stall and stop.
Depreciation of the Solex became inevitable when the Dutch government introduced obligated licenseplates for all mopeds in October 2006. The moped was reviewed by the public traffic services and I received a license plate despite the moped was not functional. So I had a second look at this vintages verhicle and started restoration. Below you can read the things I encountered.

 But first, how does a Solex look like? 

Solex OTO 63       Solex OTO 63

Note: you can click on each picture and it will enlarge to its original size (approx.2Mb).

Fuel pump

The fuel pump was broken. One of the two valve balls, responsible for the pumping effect, was missing and the plastic "crown", on which the valve balls are resting was damaged. Replacement of the fuel pump was the only option. Fortunately many parts, sometimes even new ones, are available. A new fuel pump replaced the broken one. However the new fuel pump had two disadvantages:
1. the fuel pipe coupling had another thread. In order to remove the old coupling a copper sealing sleave had to be removed using a file.
2. the new fuel pump was lacking a fuel filter. The designers of the Solex didn't place a filter in the fuel pump for the fun of it so I came up with a differend solution. Look under alternative "fuel pump filter" for more info.

Solex fuel pump The mounted fuel pump

Image Spacer on which the plastic hood is mounted. Note: the threads on the spacer is different on each side and don't forget the copper seal washer.

Image  Removal of the sealing sleeve using a file.

A disassembled, original, fuel pump:

Original Solex fuel pump disassembled  Solex fuel pump side view Solex fuel pump side view 


Fuel pump valve ball

I've seen serveral questions about the notoriuos valve balls but I've never encountered clear pictures Ik heb in de forums diversen vragen gezien over de beruchte brandstofpompkogeltjes maar nooit een duidelijk foto en/of maat gezien.

Solex fuel pump valve ball This is how a valve ball looks like.

Solex size fuel pump valve ball Diameter fuel pump valve ball of a Solex OTO is 3.96mm


Alternative fuel filter

As discribed in the previous chapter "Fuel pump" in the new replacement fuel pump isn't equiped with a fuel filter. To make sure the fuel is filtered I bought a model plane/boat miniature fuel filter. Between the fuel tank and fuel pump I removed the copper fuel pipe and placed in between the miniature filter. This type of filter is easy to remove and clean.

Solex alternative fuel pump filter Miniature filter placed between tank and fuel pump. 

Image  As you can see the filter works. Luckely the dirt is stopped in the filter.


Fuel tank cap

The Solex would stall after covering small distances. I suspected a dirty carburator but the Solex wouldn't stall if I released the fuel tank cap slightly. Conclusion a vacuum was created because air couldn't enter the fuel tank. Hidden under a thin layer of rust the air opening was found. Using a needle the rust was removed and the air inlet was opened. 

 Solex opening air inletOpening the air inlet using a needle. 


Throttle lever

Also had a closer look to the throttle lever. If you disassemble the throttle lever you're stuck with a hand full of rings. It took me half a hour to figur out where to place each ring. To prevent you from the same disaster I've taken some detailed pictures. 

Solex throttle leverSolex throttle lever  Close-up pictures of the throttle handel.


Throttle spoke

The original spoke was one big mess, so I replaced the spoke too. If you buy a new spoke the length is much too long. On the pictures you can see how long the spoke should be. Be aware that the length of the spoke depends on the height position of the handlebar.

Note: thanks to the Dutch Solex forum people noted a spring was missing near the throttle lever that keeps the spoke in position. As soon as I made this modification I will publish some new pictures on this website.

Solex throttle spokeSolex throttle spokeSolex throttle spoke Throttle spoke.



Decarbonizing the piston, outlet and inlet manifold and the opening next to the cylinder wall is now and then necessary to make sure the two stroke engine runs smoothly.
What to do? Remove the air filter en disassemble the cylinder head by unscrewing the four nuts. Remove the cylinder head and place the motor on the front wheel. By rotating the front wheel the piston will go up and down. Place the piston in the most upper position.

Solex carbonized piston Decarbonized piston in the highest position.

Removed (carefully) the deposited carbon and burned grease with for instance a screwdriver. Clean the piston head thorough after scraping of the carbon. And make sure not to damage the cylinder head gasket.

Solex decarbonized piston  A clean piston head. 

Remove the carburator and remove the outlet/inlet manifold. Place the piston in such a position that the outlet/inlet port is blocked. Now it's not possible that carbon remains drop into the crank case. Remove carbon deposits from the outlet/inlet port. Inspect the outlet pipe and remove cardon deposits if necessary.

Solex outlet manifold Outlet manifold

As last clean the opening next to the cylinder wall. Use a 5mm stealdrill for cleaning. Make sure the pistons still blocks the crank case. 

Image Cleaning the opening next to the cylinder wall.



The Solex functioned good after cleaning the engine but when driving a bumpy road the engine felt like stalling. The stalling seemed to be releated with a badly fitted part. I suspected the ignition so also was inspected more closely.
This chapter shows how to remove the flywheel and how different ignition parts look like.

Disassembling the flywheel
- remove the plastic cover that protects the flywheel remove the black rubber protection plate by removing the tringle shaped metal plate
- assemble the triangle shaped metal plate back but do not fully tighten the three bolts
- lossen the centre nut a few turns
- tighten the three bolts which holds the triangle shaped metel plate evenly. By tightening the three bolts the flywheel is pulled from it's axis.
- if the flywheel is loosend then remove the triangle shaped plate completely and flywheel nut and pull the flywheel perpendicular from it's axis

 Solex fly wheel nut Loosen the flywheel nut a few turns
 Solex flywheel plate Tighten the triangle shapped plate evenly
 Solex flywheelThe disassembled flywheel. The spline in the axis opening makes sure that the flywheel can only be assembled in one position.
 Solex ignition mechanismeThe ignition mechanisme

The contact breaker where burned. Using a file and fine sandpaper I managed to flatten and clean the contact breakers

Solex contact breaker Burned contact breakers
Solex contact breaker 

Image The ignition cable is using a spring mechanisme to make contact with the ignition coil.

The problem causing the stalling of the engine when driving over bumpy roads. The ignition wire apperendly touched the flywheel and caused an intermittent short-circuit. I replaced the white wire.

Image Worn isolation of the ignition wire  
Solex ignition coilIgnition coil

Adjusting the timing moment is done by rotating the eccentric screw. Rotating this eccentric screw the contact breakers are moved from or to each other.

Image Adjusting the timing moment by rotating the eccentric screw.

How to adjust the timing moment:
rotate the flywheel  to the right until the marking on the flywheel and crankcase match. Untighten the screws that hold the contact breaker plate slightly. Not too much otherwise the contact breaker plate will move by it's self. Place in between the contacts a sigarette paper and rotate the eccentric screw in such a way that you feel a little bit of friction when pulling out the sigarette paper. Tighten the two screws of the contact breaker plate so that it's fixed in it's position.

As reference: thickness of normal paper is approx.0.1mm, thickness of a sigarette paper is approx. 0.03mm.

Solex capacitor The capacitor. This part prevents radio/TV intereference and sparks between the contacts.


  Original guarantee card

If even have the original guarantee card. This is how it looks like: 

Solex chassis number Solex guarantee card Solex guarantee card






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