Dell'Orto PHM 40 – jetting & tuning
Large Dell'Orto range with accelerator pump; jet needles of the K series. Fitted from the factory to 8 documented models from Ducati, KTM, Moto Guzzi; with accelerator pump (pump jet).
| Make | Model | Year | Version | Designation | Reg. no. | Details |
|---|---|---|---|---|---|---|
| Ducati | 1000 Replica (Mille MHR) | 1984 | Standard | PHM 40 BS/BD | 4883/84 | view jetting |
| Ducati | 750 F1 Montjuich | 1986 | left carburettor (NS) | PHM 40 NS | 4890 | view jetting |
| Ducati | 750 F1 Montjuich | 1986 | right carburettor (ND) | PHM 40 ND | 4891 | view jetting |
| Ducati | 900 S2 | 1982 | Standard | PHM 40 BS/BD | 4865/66 | view jetting |
| Ducati | 900 SS Replica (Mike Hailwood Replica) | 1981 | left carburettor (BS) | PHM 40 BS | 4858 | view jetting |
| Ducati | 900 SS Replica (Mike Hailwood Replica) | 1981 | right carburettor (BD) | PHM 40 BD | 4859 | view jetting |
| KTM | 600 Incas | 1989 | Standard | PHM 40 SD | 4913 | view jetting |
| Moto Guzzi | 1100 Sport | 1994 | USA | PHM40NS1/ND1 | 4925/26 | view jetting |
| Moto Guzzi | 1100 Sport | 1994 | Standard | PHM40NS1/ND1 | 4923/24 | view jetting |
| Moto Guzzi | Le Mans 3 | 1982 | PHM 40 | PHM 40 DS/DD | 4869/70 | view jetting |
| Moto Guzzi | Le Mans 4 | 1984 | Standard | PHM 40 NS/ND | 4879/80 | view jetting |
| Moto Guzzi | Le Mans 4 | 1985 | USA | PHM 40 NS/ND | 4886/87 | view jetting |
| Moto Guzzi | Le Mans 4 | 1988 | Germany / Austria | PHM 40 NS/ND | 4903/04 | view jetting |
| Moto Guzzi | Le Mans 4 | 1988 | Italy | PHM 40 NS/ND | 4895/96 | view jetting |
| Make | Ducati | Ducati | Ducati | Ducati | Ducati | Ducati | KTM | Moto Guzzi | Moto Guzzi | Moto Guzzi | Moto Guzzi | Moto Guzzi | Moto Guzzi | Moto Guzzi |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Model | 1000 Replica (Mille MHR) | 750 F1 Montjuich | 750 F1 Montjuich | 900 S2 | 900 SS Replica (Mike Hailwood Replica) | 900 SS Replica (Mike Hailwood Replica) | 600 Incas | 1100 Sport | 1100 Sport | Le Mans 3 | Le Mans 4 | Le Mans 4 | Le Mans 4 | Le Mans 4 |
| Year | 1984 | 1986 | 1986 | 1982 | 1981 | 1981 | 1989 | 1994 | 1994 | 1982 | 1984 | 1985 | 1988 | 1988 |
| Version | Standard | left carburettor (NS) | right carburettor (ND) | Standard | left carburettor (BS) | right carburettor (BD) | Standard | USA | Standard | PHM 40 | Standard | USA | Germany / Austria | Italy |
| Designation | PHM 40 BS/BD | PHM 40 NS | PHM 40 ND | PHM 40 BS/BD | PHM 40 BS | PHM 40 BD | PHM 40 SD | PHM40NS1/ND1 | PHM40NS1/ND1 | PHM 40 DS/DD | PHM 40 NS/ND | PHM 40 NS/ND | PHM 40 NS/ND | PHM 40 NS/ND |
| Reg. no. | 4883/84 | 4890 | 4891 | 4865/66 | 4858 | 4859 | 4913 | 4925/26 | 4923/24 | 4869/70 | 4879/80 | 4886/87 | 4903/04 | 4895/96 |
| Details | view jetting | view jetting | view jetting | view jetting | view jetting | view jetting | view jetting | view jetting | view jetting | view jetting | view jetting | view jetting | view jetting | view jetting |
| Model | Year | Main jet | Pilot jet | Starter jet | Needle (clip) | Atomiser | Slide |
|---|---|---|---|---|---|---|---|
| Ducati 1000 Replica (Mille MHR) | 1984 | 125 | 65 | 60 | K 5 (2) | 265 AB | 60/1 |
| Ducati 750 F1 Montjuich – left carburettor (NS) | 1986 | 155 | 65 | 60 | K 5 (2) | 265 AB | 60/1 |
| Ducati 750 F1 Montjuich – right carburettor (ND) | 1986 | 148 | 65 | 60 | K 5 (2) | 265 AB | 60/1 |
| Ducati 900 S2 | 1982 | 135 | 65 | 60 | K 5 (2) | 265 AB | 60/1 |
| Ducati 900 SS Replica (Mike Hailwood Replica) – left carburettor (BS) | 1981 | 140 | 65 | 60 | K 5 (2) | 265 AB | 60/1 |
| Ducati 900 SS Replica (Mike Hailwood Replica) – right carburettor (BD) | 1981 | 135 | 65 | 60 | K 5 (2) | 265 AB | 60/1 |
| KTM 600 Incas | 1989 | 195 | – | 45 | K 51 (2) | 272 DR | 40 |
| Moto Guzzi 1100 Sport (USA) | 1994 | 152 | 52 | 60 | K27 (2) | 265 AB1 | 503 |
| Moto Guzzi 1100 Sport | 1994 | 152 | 57 | 60 | K18 (3) | 266 AB | 605 |
| Moto Guzzi Le Mans 3 – PHM 40 | 1982 | 170 | 60 | – | K 4 (2) | 265 AB | 601 |
| Moto Guzzi Le Mans 4 | 1984 | 145 | 57 | 60 | K 19 (3) | 268 AB | 605 |
| Moto Guzzi Le Mans 4 (USA) | 1985 | 150 | 62 | 60 | K 33 (3) | 260 AB1 | 503 |
| Moto Guzzi Le Mans 4 (Germany / Austria) | 1988 | 145 | 57 | 60 | K 19 (3) | 266 AB | 605 |
| Moto Guzzi Le Mans 4 (Italy) | 1988 | 145 | 57 | 60 | K 19 (3) | 268 AB | 605 |
| Model | Ducati 1000 Replica (Mille MHR) | Ducati 750 F1 Montjuich – left carburettor (NS) | Ducati 750 F1 Montjuich – right carburettor (ND) | Ducati 900 S2 | Ducati 900 SS Replica (Mike Hailwood Replica) – left carburettor (BS) | Ducati 900 SS Replica (Mike Hailwood Replica) – right carburettor (BD) | KTM 600 Incas | Moto Guzzi 1100 Sport (USA) | Moto Guzzi 1100 Sport | Moto Guzzi Le Mans 3 – PHM 40 | Moto Guzzi Le Mans 4 | Moto Guzzi Le Mans 4 (USA) | Moto Guzzi Le Mans 4 (Germany / Austria) | Moto Guzzi Le Mans 4 (Italy) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Year | 1984 | 1986 | 1986 | 1982 | 1981 | 1981 | 1989 | 1994 | 1994 | 1982 | 1984 | 1985 | 1988 | 1988 |
| Main jet | 125 | 155 | 148 | 135 | 140 | 135 | 195 | 152 | 152 | 170 | 145 | 150 | 145 | 145 |
| Pilot jet | 65 | 65 | 65 | 65 | 65 | 65 | – | 52 | 57 | 60 | 57 | 62 | 57 | 57 |
| Starter jet | 60 | 60 | 60 | 60 | 60 | 60 | 45 | 60 | 60 | – | 60 | 60 | 60 | 60 |
| Needle (clip) | K 5 (2) | K 5 (2) | K 5 (2) | K 5 (2) | K 5 (2) | K 5 (2) | K 51 (2) | K27 (2) | K18 (3) | K 4 (2) | K 19 (3) | K 33 (3) | K 19 (3) | K 19 (3) |
| Atomiser | 265 AB | 265 AB | 265 AB | 265 AB | 265 AB | 265 AB | 272 DR | 265 AB1 | 266 AB | 265 AB | 268 AB | 260 AB1 | 266 AB | 268 AB |
| Slide | 60/1 | 60/1 | 60/1 | 60/1 | 60/1 | 60/1 | 40 | 503 | 605 | 601 | 605 | 503 | 605 | 605 |
“–” means: not fitted on this model, or not documented in the source.
Important: figures apply to standard condition
These factory figures apply to standard condition with the original air filter and original exhaust. Any modification (open bellmouths, different exhaust, camshaft …) changes the airflow and calls for a revised setup.
Compiled from several sources – chiefly official Dell'Orto application catalogues and original workshop manuals – and cross-checked against factory tables and community knowledge. Details: Sources & method.
Tuning guide: running lean / running rich
First narrow down the load range in which the problem occurs — then it is clear which part is responsible. The mapping follows Dell'Orto tuning literature and the Moto Guzzi workshop manuals: from idle to roughly 1/4 throttle the pilot jet and mixture screw are in charge, from roughly 1/8 to 3/4 throttle the jet needle (clip position) and atomiser, and from roughly 1/2 throttle to full load the main jet.
| Symptom | Load range | Responsible | Direction |
|---|---|---|---|
| Pale, greyish-white plugs; flat and gutless at the top end; overheating | from ~1/2 to full throttle | main jet | try one size larger |
| Runs better on choke; popping/banging on the overrun | idle to ~1/4 | pilot jet + mixture screw (check for air leaks first) | richer: larger jet or screw further out |
| Hesitation/flat spot when opening the throttle | transition (accelerator pump) | pump jet/pump function, then needle position | richen, check function |
| Surging/leaning out at steady speed and mid throttle | ~1/8 to 3/4 | jet needle (clip) and atomiser | raise the needle one notch (clip lower) = richer |
| Sooty black plugs; burbling running; smell of fuel; high consumption | narrow it down: idle ↔ mid ↔ full | depending on range: pilot jet / needle + atomiser / main jet | leaner: smaller jet or needle lower |
| Gets worse the hotter the engine runs | usually idle/part throttle | overall setup too rich; also check float level | lean it out, check the float height |
Always change in single steps (“one or two jet sizes, then check the plug colour”), judge only on a warmed-up engine and make just one change per test ride. Your anchor is always the factory value for your model (table above) — on the PHM 40 the documented factory main jets range from 125 to 195. Work from there in single steps in the diagnosed direction.
These notes do not replace a proper check. When in doubt use a lambda meter, a dyno or a specialist workshop – an engine running lean for long periods can be damaged.
Matching jet set
A set around the factory value (main jets in steps either side) covers the range you need while dialling in – only a test on the engine shows the final size. Ready-made sets per model are in preparation.
Matching parts for Dellorto PHM 40
Parts that are usually replaced when overhauling this carburettor range.
Real-world setups from the community
Documented setups from forums, summarised in our own words and linked. They show what people actually ran on specific conversions – they are not a recommendation and do not replace your own testing.
User report, no warranty — not a factory figure
Moto Guzzi 1000 S — PHM 40
Condition/modifications: Standard airbox, twin-plug ignition
Jetting used: Main jet 155, pilot jet 55, throttle slide 60, atomiser and needle standard
Result according to the report: User reports unremarkable running, consumption around 4.3 l/100 km, normal engine temperatures (90–100 °C oil).
Source: groups.google.com
Further reading
Frequently asked questions
What does the atomiser do and why does it matter so much?
The atomiser (also called the needle jet or emulsion tube) is the sleeve the jet needle runs in. Together with the needle it governs the mixture in the part-throttle range — exactly where you ride almost all the time. Experienced tuners rate it at least as important as the main jet: a single step (say 262 to 264) changes how the bike rides noticeably. With Dell'Orto the number is the bore and the letters are the design (e.g. AB, AR).
Discussion: caferacer-de
What does the needle clip position do?
The needle hangs from the throttle slide and its taper opens up the cross-section in the atomiser. Move the clip one notch down (needle sits higher) and the part-throttle range gets richer, one notch up (needle lower) leans it out. The factory figure counts the notches from the top. The needle position acts roughly between 1/4 and 3/4 throttle — not at idle and barely at full throttle.
Discussion: caferacer-de
How do I set the mixture screw correctly?
As a starting point the Moto Guzzi workshop manuals for the carburettor models consistently give 1.5 turns out from lightly seated. Fine tuning on a warmed-up engine: turn the mixture screw on each cylinder slowly until the engine runs at its smoothest and fastest, then correct the idle speed and synchronise both carburettors. If the engine only runs cleanly at well over two turns, the pilot jet is usually too small or the circuit is dirty.
Discussion: 2-ventiler.de
The engine hesitates when I open the throttle — why?
When the slide is opened quickly the mixture leans out briefly. PHF and PHM have an accelerator pump for exactly that — if the engine hesitates, its pump jet is often blocked, the diaphragm is damaged, or the idle-to-needle transition is too lean. On carburettors without a pump (e.g. VHB, PHBH) only a clean transition setup helps. Check the mundane causes too: float level, fuel supply, worn slides.
Discussion: 2-ventiler.de
Do both carburettors need the same jetting?
Yes. Both cylinders need the same set of jets, and the factory figures always apply per carburettor. After every job the pair belongs synchronised (same slide lift, same mixture screw setting), otherwise one cylinder runs richer than the other and the plug colour becomes unreadable. Unequal jetting is almost always a sign of a previous owner tinkering.
Discussion: 2-ventiler.de