The 1978 Alfa Romeo Spider Veloce is fitted with a complete set of Solex 40 ADDHE carburettors, a familiar system for anyone who works with classic Italian engines. These carburettors were designed for sporty four-cylinder engines and give the Spider its characteristic throttle response, but they call for precise maintenance and a correct setup.
What is the Solex 40 ADDHE?
The Solex 40 ADDHE is a twin-choke sidedraught carburettor, intended for sports engines running at higher revs. The "40" stands for the diameter of the venturi, which determines how much air the engine can draw in. The ADDHE series is used mainly on Italian cars because they respond so well to quick throttle changes and free-revving engines. The design consists of two throttle butterflies per carburettor, a piston-controlled mixture system and a series of interchangeable jets that determine the fuel delivery.
How does the system work on an Alfa Romeo Spider Veloce (1978)?
The 2.0-litre engine of the Spider Veloce was designed to make the most of these carburettors. The ADDHEs deliver direct throttle response, predictable mixture behaviour and strong performance at higher revs. The combination of mechanical throttle butterflies, accelerator pumps and venturis makes the engine pick up eagerly, provided everything is set up correctly.
Common points to watch on the Solex 40 ADDHE
Owners of classic Alfas often recognise the same points:
- Worn spindles and throttle shafts. This causes air leaks, which lead to a rough idle and a setup that is difficult to get right.
- Aged gaskets and diaphragms. Fuel ageing makes the rubbers harden, which causes leaks and keeps the carburettor from working at its best.
- Dirty jets or blocked internal passages. Dirt build-up is very common, especially on cars that cover few miles.
- Synchronisation issues. Both carburettors must open exactly in step; any deviation gives immediately noticeable vibrations and poor throttle response.
- Wear on the float needle and seat. This affects the fuel level in the float chamber and with it the mixture.
Why an overhaul is essential
The Solex 40 ADDHE works superbly when all its parts are within specification. On classics that are many years old, an overhaul is often necessary. A professional overhaul ensures the correct fuel level, a correct throttle setting, reliable diaphragms and gaskets, proper synchronisation and a stable idle with predictable response.
Carburateur Service Nederland, specialists in classic Solex systems
Do you own an Alfa Romeo Spider Veloce? Then we take on your Solex 40 ADDHE completely: ultrasonic cleaning, replacing wear parts, synchronising and setting it up on your engine. We work precisely to the factory specifications, so your Solex does its job crisply again.