Carburettor and fuel system service in Cascais: ultrasonic cleaning, rebuild and electronic synchronisation

One page for everything between the fuel tap and the combustion chamber: carburettors, fuel injectors, throttle bodies, fuel lines and filters. The prices below are labour, taken from the 2026 price list, and cover the work on the carburettor itself; taking the carburettors off the motorcycle, refitting them and synchronising are quoted separately in the same written estimate, as are sealing kits, jets, needles and other parts — approved by you before anything is ordered.

A carburettor has no electronics to fail; what fails is the fuel and the passages it flows through. Petrol left standing evaporates within weeks and leaves gum and varnish behind. Pump petrol in Europe contains up to 10 % ethanol (E10): ethanol absorbs water from the air, separates out at the bottom of the float bowl and corrodes aluminium and zinc alloys into white oxide, while it hardens and swells old rubber. A pilot jet is a few tenths of a millimetre across — it is the first passage to block, and a bike that stood for a few months over winter can already show it.

The symptoms are familiar to anyone who rides a carburetted bike:

• hard starting, especially cold, and a long warm-up on choke;
• an idle that hunts, drops or needs the throttle held open;
• hesitation just off idle, flat spots, popping on the overrun;
• a smell of petrol, or fuel dripping from the overflow — a float needle that no longer seals;
• one cylinder cold at idle on a twin or a four, and more vibration than the bike used to have;
• black spark plugs and consumption that has crept up.

Carburettor cleaner through the bowl drain and a new set of plugs rarely fix any of this for long, because the deposits sit inside drillings a spray cannot reach. That is why we strip the carburettor and put the bare body in the ultrasonic bath.

Ultrasonic cleaning works by cavitation. Transducers under the tank vibrate the heated cleaning solution tens of thousands of times per second; microscopic bubbles form and collapse against the metal, and that collapse lifts varnish, gum and oxide out of every drilling, emulsion tube and jet — including the passages no brush, wire or spray can enter. The process is non-abrasive: threads, jet orifices and sealing faces keep their exact geometry, which matters, because a jet opened up with a drill bit is a jet with the wrong number.

We use a professional ultrasonic bath with professional cleaning agents chosen for aluminium carburettor bodies and brass jets — not a household degreaser, which can attack the alloy. After the bath every passage is blown through with compressed air and checked against the light.

The video on this page shows the bath and the synchronisation on a real customer bike.

On an engine with more than one carburettor or throttle body, every cylinder has its own intake, and each must open by exactly the same amount — at idle and as the throttle moves. If one opens earlier, that cylinder carries more of the load: the idle hunts, the bike vibrates, response is rough at small throttle openings and one cylinder runs hotter than its neighbours.

Synchronisation measures the intake vacuum of every cylinder at the same time and adjusts the linkage until the readings match within the manufacturer's tolerance. We do it with electronic gauges, which resolve differences a mechanical gauge cannot show and display the pulsing of each cylinder in real time. It is the last step of every carburettor rebuild here; it is needed after any carburettor or throttle-body removal; and it is worth doing on its own on a bike that runs but idles unevenly — on carburettors and on the throttle bodies of fuel-injected engines alike.

Injectors fail more quietly than carburettors. Deposits on the nozzle and pintle turn a fine cone of spray into a stream, reduce the flow of one injector against its neighbours and let fuel dribble after the injector should have closed. The engine management compensates up to a point, which is why the symptoms — rough idle, hesitation, higher consumption, a misfire under load — arrive late.

We remove the injectors, clean them ultrasonically and run each one through more than ten checks on the test bench, among them:

• spray pattern at idle and at higher pulse widths — a cone, not a jet or a dribble;
• flow at several pulse widths, static and pulsed;
• delivery compared across the set — the injectors of one engine should be within a few per cent of each other;
• leak-tightness under system pressure with the injector closed;
• coil resistance and opening response at low duty;
• a before-and-after comparison, so you can see what changed.

Filters and seals are renewed where needed. An injector that cannot be brought back to specification is named as such, with the price of a replacement in writing.

Most of the carburettors on our bench are Keihin, Mikuni, Dell'Orto, Bing and S&S units — a single carburettor on a big twin or a single, banks of two, three and four on multi-cylinder engines, slide and constant-velocity (CV) types. Typical bikes: carburetted Harley-Davidson models with the CV carburettor and S&S conversions; Japanese fours and twins of the 1980s to 2000s (Honda, Suzuki and others); Triumph Bonneville, Thruxton and Scrambler of the carburetted years; Royal Enfield before fuel injection; BMW airheads with Bing carburettors; Ducati and Moto Guzzi carburetted models. On fuel-injected motorcycles the same page covers throttle-body synchronisation and injector service. Classic, modern and custom bikes alike.

We're in São Domingos de Rana, Cascais municipality, Greater Lisbon — a short ride from Estoril, Carcavelos, Parede, Oeiras, Sintra and Lisbon. If the bike doesn't run, the carburettors can come in on their own for cleaning and rebuilding; synchronisation needs the engine, so the last step happens with the bike here. For a bike that stood all winter, carburettor service pairs naturally with the pre-season check on the price list. Send the model, the year, the number of carburettors and a sentence about what the bike is doing — that is enough for a first answer.