How many jets are in a Honda 50 hp four-stroke carburettor, and where does the loose small jet go?
I have a Honda 50 hp four-stroke, serial number BAZS-3210088, and I have taken the carburettors apart for cleaning. One very small brass jet is out, and I cannot work out where it belongs. How many jets should there be in each carburettor?
Answer
A carburetted Honda BF50 has three carburettors, each with a main fuel jet and slow-running metering components, but the number of removable jets depends on the carburettor version. The loose small brass piece could belong to the slow-running, air-bleed or starting circuit; check its shape against the correct carburettor diagram before fitting it.
Check the carburettor identification
Find the engine identification plate and the marking stamped on the carburettor body. Give a Honda Marine parts supplier the complete serial number, BAZS-3210088, and the carburettor marking. Horsepower alone does not identify the correct jet arrangement.
BF50 carburettor specifications differ between production versions and markets. A previous owner may also have fitted a replacement carburettor assembly. Later fuel-injected BF50 engines do not use these carburettor jets.
Ask for the exploded carburettor drawing and parts list for the engine. Before swapping parts between the upper, middle and lower carburettors, check whether they have different part numbers or jet specifications.
Disconnect the fuel supply and drain petrol into a suitable container. Work in a ventilated area away from sparks or flames.
Which parts count as jets
There is no universal answer of "two" or "three": the count depends on which parts are included. You are likely to find:
- Main jet: a short brass metering piece, usually with a screwdriver slot and a calibrated central hole. Remove the float bowl to reach it.
- Main nozzle or emulsion tube: a longer tube associated with the main jet, often with several side holes. It is a separate component but is not necessarily listed as another jet.
- Slow-running jet or jet set: the component with small passages that supplies the idle and progression circuit. Honda's parts terminology and the component's construction vary by version.
- Air-bleed or starting-circuit metering parts: additional restrictions that may be fixed in the casting or separately removable.
The pilot mixture screw is an adjustment screw, not a loose interchangeable jet. Its tapered tip, spring and any washer or seal distinguish it from a simple metering insert.
Locate the loose brass piece
Do not choose a hole simply because the thread fits. A small brass component can screw into the wrong position and leave a fuel circuit incorrectly metered.
Establish its position in this order: