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Introduction and Tips

For most veteran enthusiasts, the technical aspects of the hobby are all-important. Our technical pages deal with technical principles and significant technical trends of the past.

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When you have acquired an old moped, check that everything is in working order before attempting to start it. Though this may take some time, you may well save yourself a lot of trouble later.

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Proceed systematically. Start by finding out how everything should function. If possible, get hold of relevant literature (manuals etc.). Then find out if everything works as it should, and remedy any faults you find.

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If you want a reliable moped, making sure that every part of the engine is in good working order is key.

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A note to the younger readers: if you want to successfully beef up your engine, it will have to be in good working order to start with. This is absolutely crucial. Otherwise you’ll simply end up with a very noisy engine which will cause you nothing but trouble.

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Fuel Supply

Check:

That you have enough petrol in your tank.

That the supply to the carburettor isn’t blocked.

That there is no water in the petrol.

That a vacuum isn’t created in the tank when petrol is consumed.

That the carburettor is clean and free of water. Cleaning a carburettor is a fairly tricky job, and you risk making any blockages worse (especially if you use compressed air), so work carefully.

If the moped hasn’t run for a long time, all petrol in the tank must be changed. Often mopeds that haven’t run for even a single season won’t start until fresh petrol has been put in the tank.

Make a rough adjustment of the air/petrol mix before starting, and fine tune when the engine is warm.

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The Filling of the Combustion Chamber

The inlet filter/air filter must be clean. Pipes and tubes must be absolutely leak-free all the way from the exhaust silencer can to the carburettor.

The carburettor must be securely mounted on the inlet manifold.

The gasket between the inlet pipe and cylinder must be perfectly aligned to the inlet holes so as not to cause unwanted resistance.

The same applies to the crankcase-cylinder gasket as for the inlet gasket: Nothing must obstruct the transfer ports. Be extremely cautious with liquid gasket as it is difficult to predict where it will go. If you must use it, apply a very thin layer only.

Make sure the inside of exhaust system is free of coke and oil residue, and that all parts are securely mounted with no leakages at the joints. Also check for non-original holes.

Check that the inlet diaphragms seal properly (not all mopeds have these).

The piston crown, the exhaust port and the inside of the cylinder head must be free of coke residue. Be extremely careful not to scratch the metal when removing coke residue. Any scratches will cause coke residue to build up more rapidly.

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Compression in the Combustion Chamber

It is imperative that compression in the combustion chamber is sufficiently high. Unless your moped is of the type that needs no cylinder head gasket, use a thin aluminium gasket.

Also, check the cylinder, piston and piston rings for wear.

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Crank Compression

A small but crucial detail that is often overlooked is that crank compression must also be sufficiently high. Too low under compression is often caused by old and stiff/worn zimmer rings on the crankshaft. Make sure these are okay.

Also check:

That the connection between the crack case and cylinder is air-tight.

The crankcase for cracks.

The gaskets between the various parts of the engine block, the crankcase-cylinder gasket and the inlet gasket and manifold.

The cylinder, which may have cracks in it, from a transfer ports to the open air for instance.

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Ignition

You should have a good strong spark. Check the spark plug and the ignition in general. Dampness can easily cause ignition problems.

If the ignition is in good working order the spark plug will give a strong, healthy spark when you turn the engine over by hand (I can start my moped in this way).

Adjust the ignition so that the contact breaker gap is somewhere between 0.3 and 0.4 mm when fully open. The point of ignition is usually 1-2 mm before top dead centre position.

The distance between the electrodes on the spark plug should be 0.5mm, or as specified by the manufacturer.

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Also make sure that:

There is oil in the gearbox.

That the chain and sprockets are well lubricated.

That wheel bearings are okay and are well lubricated.

That the brakes function perfectly and don’t bind.

That the tyres are properly inflated.

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Running the Engine in

If the engine needs running in, I recommend using a 4% mixture (40ml to the litre) for the first 3 tanks, and then going down to 2%. Use proper two-stroke oil. Any other type of oil in the petrol can/will give various problems, which I will not go into here.

The most important thing to bear in mind when running in is that engine mustn’t be pushed too hard. This can simply be avoided by not giving full throttle until the engine has run for about an hour.