Moto Guzzi Le Mans 1
Figures apply to standard condition with the original air filter and exhaust. The year comes from the factory document and is not a production range: if your bike is a different year of the same version, these figures are your starting point.
Source and checks
- Moto Speziale table, page 1, data row 39; sales designation: “LM1,2”
- Cross-checked: Dokumentierte Diskrepanz der Originalunterlagen zur Le Mans 1, via Community-Recherche (guzzisti.de, Thread 9230 “Le Mans 1 Vergaser – korrekte Bedüsung PHF 36 B”, Abruf 24.07.2026)
- Main jet: Moto Speziale factory table “140”, further original documents, see FAQ “145 (parts list) or 135 (owner's manual) — per documented community analysis of the original documents”. We show both and don't decide ourselves.
- Needle: Moto Speziale factory table “K5”, further original documents, see FAQ “K8 (parts list) or K5 (owner's manual) — per documented community analysis”. We show both and don't decide ourselves.
- Sources & method
Complete carburettor
PHF 36 DD1€264.95PHF 36 DS1€264.95Current Dell'Orto version. It may differ from your original (PHF36BS/BD); set the jetting to the figures above afterwards.
Matching parts from our stock exactly for this jetting
Idle jet 60Dellorto Leerlaufdüse 5mm, 60€2.15Ships immediately
Needle jet 265ABDellorto Zerstäuber AB 265€11.50Ships immediately
Throttle slide 603Dellorto Gasschieber PHF 60/3€75.90Ships immediately
Float valve 300Dellorto Nadelventil PH... Serien 300€19.95Ships immediately
Starter jet 70Dellorto Starterdüse 70€5.10Ships immediatelyMore spare parts for Dell'Orto PHF
Part not listed?
Dell'Orto supplies almost everything. Just ask, we'll take care of it.
Not running right?Pick the symptom, we show the part responsible.
Pale, greyish-white plugs; flat and gutless at the top end; overheating
Runs better on choke; popping/banging on the overrun
Hesitation/flat spot when opening the throttle
Surging/leaning out at steady speed and mid throttle
Sooty black plugs; burbling running; smell of fuel; high consumption
Gets worse the hotter the engine runs
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.
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.
Further reading
Frequently asked questions
Le Mans 1: which factory jetting is actually correct?
For the Le Mans 1 the original documents contradict each other — that is a documented problem, not a gap in this database: the parts list gives main jet 145 with needle K8, the owner's manual 135 with K5, the Moto Speziale factory table 140 with K5, and an erratum in the Le Mans III workshop manual declares its figures (main jet 115) valid for the Le Mans II as well. Every version is documented on the Le Mans 1 page. In practice this means: take the factory figure as your starting point and verify it on your own engine.
Discussion: guzzisti.de
The spark plugs are black and sooty — what should I do?
Sooty black plugs show a mixture that is too rich. Which circuit is responsible depends on where the bike runs rich: at idle and steady speed it is more likely the pilot jet and mixture screw, in the mid range the needle position and atomiser, at full throttle the main jet. Also check for a sticking choke, the float level, a leaking float needle valve and an oil-soaked air filter. Change one step at a time and check the plug colour after every change.
Discussion: guzzisti.de
Air filter or exhaust modified — what jetting do I need now?
There is no blanket figure, and nobody can name one honestly without testing. More open intakes and exhaust systems lean out the mixture, so the setup has to go richer, usually starting with the main jet and often at the needle/atomiser too. Real-world reports show: the factory value is your anchor, and from there you test in steps (plug colour and how it rides, better still a lambda reading). Concrete community examples with full context are on the carburettor pages under “Real-world setups”.
Discussion: groups.google.com
In what order do I tune a Dell'Orto?
The proven order: full throttle first (main jet), then part throttle (needle position, atomiser if needed), and idle last (pilot jet and mixture screw) — and above all: only one change per step, tested on a warmed-up engine. The reason: the circuits overlap, and a wrong main jet falsifies any part-throttle judgement. The detailed procedure is in the guide “Tuning a Dell'Orto step by step” (German).
Discussion: caferacer-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