The engines of Solex are by their simplicity and their exemplary accessibility easy to modify to gain in couple and power. Of course, the transmission by roller will acknowledge its limits and the announced consumption of 1,4l/100km of S3800 will be nothing any more but one to remember...
There are our our days some competitions official where racing cars more or less modified in various categories clash which depend on the improvements carried out. The fastest machines sink at a speed higher than 100km/h with an engine in low position under the framework (standard Mobylette). Certain races relate on the endurance or consumption. To know some more about the subject, to refer in the page of bonds.

To gain in power and couple, it is necessary either to increase the quantity of fuel per explosion, or to increase compression or or to improve lighting. (or 3 at the same time besides!).
Below some councils follow but so certain readers have photographs and councils interesting, I will add them readily.

Compression

To increase compression amounts decreasing the place in the combustion chamber, i.e. the zone delimited by the walls of the cylinder, the piston in high position and the cylinder head. The cylinder and the piston-rod unit must be preserved to satisfy the requirements of the 50cc max. The solution lies in the machining of the cylinder head of which the part pressing on the cylinder can be somewhat machined. It will then be necessary to pay attention so that the candle and the ordering of decompression do not come into contact with the piston at the time of its increase. This solution is not infinite bus with the top of a certain compression, the air-gasoline mixture car-inflamme before the complete rise of the piston (catastrophic and dangerous!).
This handling is of course to make with people who already did them.

Fuel

There are there several solutions, simplest being to adapt a larger carburettor to replace that of origin the purpose of which was principal, point out it, the economy. The problem which then will arise and limited capacity of the petrol station and limited quantity of consumable mixture by of the cylinder-piston unit. Indeed, since the rise of the piston creates an aspiration in the casing which leaves free the entry of the mixture when the piston is in high position and conversely, the descent of the piston entraine by compression in the casing the passage of the mixture in the top of the cylinder by the lights of the cylinder, these passages being of size optimized for low fuel consumption.
All thus depends on waitings of the modifications. In fact, the increase in the size of the jet or carburettor remains limited in configuration of origin due to place and design. For a more important profit in power, the recourse to carburettor with the use of one limps with valves gone up directly on the casing lateral of the engine. The tank must thus be moved but the petrol station of origin becomes useless.
The internal circuit of the gasoline in the engine can be modified by modifying the skirt of the piston.