Dell'Orto PHBH 26 – jetting & tuning
Dell'Orto range without accelerator pump; jet needles of the X series. Fitted from the factory to 15 documented models from Aprilia, Peugeot.
| Make | Model | Year | Version | Designation | Reg. no. | Details |
|---|---|---|---|---|---|---|
| Aprilia | Custom 88 | 1988 | Standard | PHBH 26 RS | 4025 | view jetting |
| Aprilia | ETX Enduro | 1984 | Standard | PHBH 26 BS | 3386 | view jetting |
| Aprilia | Trial 320 (Motor Hiro) | 1981 | Standard | PHBH 26 BS | 3358 | view jetting |
| Aprilia | Trial TX 300 | 1985 | Standard | PHBH 26 BS | 3411 | view jetting |
| Aprilia | Trial TX 311 (240 cc) M/86 | 1986 | Standard | PHBH 26 BS | 3439 | view jetting |
| Aprilia | Trial TX 311/87 | 1986 | Standard | PHBH 26 PS | 3474 | view jetting |
| Aprilia | Trial TX 312/88 | 1987 | Standard | PHBH 26 CS | 4013 | view jetting |
| Aprilia | Trial TXM 300/86 | 1985 | Standard | PHBH 26 BS | 3440 | view jetting |
| Aprilia | Trial TXR 312 (240 cc) M/88 (Frankreich) | 1988 | Standard | PHBH 26 CS | 4014 | view jetting |
| Aprilia | Trial/89 Climber H₂O | 1988 | Standard | PHBH 26 CS | 4034 | view jetting |
| Aprilia | Tuareg 125 ETX | 1986 | Standard | PHBH 26 NS | 3454 | view jetting |
| Peugeot | TXE Esport. | 1982 | Standard | PHBH 26 AS | 3362 | view jetting |
| Peugeot | TXT Esport. | 1983 | Standard | PHBH 26 AS | 3369 | view jetting |
| Peugeot | X123 Enduro | 1984 | Standard | PHBH 26 BS | 3408 | view jetting |
| Peugeot | X123 Enduro | 1985 | Standard | PHBH 26 BS | 3437 | view jetting |
| Peugeot | X200 AR | 1985 | Standard | PHBH 26 BS | 3427 | view jetting |
| Make | Aprilia | Aprilia | Aprilia | Aprilia | Aprilia | Aprilia | Aprilia | Aprilia | Aprilia | Aprilia | Aprilia | Peugeot | Peugeot | Peugeot | Peugeot | Peugeot |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Model | Custom 88 | ETX Enduro | Trial 320 (Motor Hiro) | Trial TX 300 | Trial TX 311 (240 cc) M/86 | Trial TX 311/87 | Trial TX 312/88 | Trial TXM 300/86 | Trial TXR 312 (240 cc) M/88 (Frankreich) | Trial/89 Climber H₂O | Tuareg 125 ETX | TXE Esport. | TXT Esport. | X123 Enduro | X123 Enduro | X200 AR |
| Year | 1988 | 1984 | 1981 | 1985 | 1986 | 1986 | 1987 | 1985 | 1988 | 1988 | 1986 | 1982 | 1983 | 1984 | 1985 | 1985 |
| Version | Standard | Standard | Standard | Standard | Standard | Standard | Standard | Standard | Standard | Standard | Standard | Standard | Standard | Standard | Standard | Standard |
| Designation | PHBH 26 RS | PHBH 26 BS | PHBH 26 BS | PHBH 26 BS | PHBH 26 BS | PHBH 26 PS | PHBH 26 CS | PHBH 26 BS | PHBH 26 CS | PHBH 26 CS | PHBH 26 NS | PHBH 26 AS | PHBH 26 AS | PHBH 26 BS | PHBH 26 BS | PHBH 26 BS |
| Reg. no. | 4025 | 3386 | 3358 | 3411 | 3439 | 3474 | 4013 | 3440 | 4014 | 4034 | 3454 | 3362 | 3369 | 3408 | 3437 | 3427 |
| 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 | view jetting | view jetting |
| Model | Year | Main jet | Pilot jet | Starter jet | Needle (clip) | Atomiser | Slide |
|---|---|---|---|---|---|---|---|
| Aprilia Custom 88 | 1988 | 108 | 52 | 70 | X 15 (3) | 262 DG | 50 |
| Aprilia ETX Enduro | 1984 | 92 | 52 | 70 | X 17 (3) | 260 AV | 40 |
| Aprilia Trial 320 (Motor Hiro) | 1981 | 103 | 50 | 65 | X 13 (2) | 266 AV | 60 |
| Aprilia Trial TX 300 | 1985 | 88 | 55 | 65 | X 2 (2) | 264 AV | 40 |
| Aprilia Trial TX 311 (240 cc) M/86 | 1986 | 88 | 52 | 65 | X 5 (2) | 266 BN | 40 |
| Aprilia Trial TX 311/87 | 1986 | 88 | 60 | 65 | X 17 (2) | 266 BN | 50 |
| Aprilia Trial TX 312/88 | 1987 | 85 | 55 | 65 | X 50 (3) | 266 BN | 50 |
| Aprilia Trial TXM 300/86 | 1985 | 88 | 48 | 65 | X 5 (2) | 266 BN | 40 |
| Aprilia Trial TXR 312 (240 cc) M/88 (Frankreich) | 1988 | 90 | 58 | 65 | X 50 (3) | 266 BN | 45 |
| Aprilia Trial/89 Climber H₂O | 1988 | 100 | 45 | 70 | X 24 (2) | 262 EM | 55 |
| Aprilia Tuareg 125 ETX | 1986 | 103 | 50 | 70 | X 16 (3) | 264 DG | 40 |
| Peugeot TXE Esport. | 1982 | 100 | 55 | 60 | X 23 (2) | 262 M | 40 |
| Peugeot TXT Esport. | 1983 | 102 | 55 | 60 | X 19 (2) | 262 CH | 40 |
| Peugeot X123 Enduro | 1984 | 102 | 55 | 65 | X 34 (2) | 260 CV | 40 |
| Peugeot X123 Enduro | 1985 | 100 | 55 | 70 | X 35 (2) | 260 DF | 40 |
| Peugeot X200 AR | 1985 | 105 | 52 | 70 | X 34 (2) | 260 CV | 50 |
| Model | Aprilia Custom 88 | Aprilia ETX Enduro | Aprilia Trial 320 (Motor Hiro) | Aprilia Trial TX 300 | Aprilia Trial TX 311 (240 cc) M/86 | Aprilia Trial TX 311/87 | Aprilia Trial TX 312/88 | Aprilia Trial TXM 300/86 | Aprilia Trial TXR 312 (240 cc) M/88 (Frankreich) | Aprilia Trial/89 Climber H₂O | Aprilia Tuareg 125 ETX | Peugeot TXE Esport. | Peugeot TXT Esport. | Peugeot X123 Enduro | Peugeot X123 Enduro | Peugeot X200 AR |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Year | 1988 | 1984 | 1981 | 1985 | 1986 | 1986 | 1987 | 1985 | 1988 | 1988 | 1986 | 1982 | 1983 | 1984 | 1985 | 1985 |
| Main jet | 108 | 92 | 103 | 88 | 88 | 88 | 85 | 88 | 90 | 100 | 103 | 100 | 102 | 102 | 100 | 105 |
| Pilot jet | 52 | 52 | 50 | 55 | 52 | 60 | 55 | 48 | 58 | 45 | 50 | 55 | 55 | 55 | 55 | 52 |
| Starter jet | 70 | 70 | 65 | 65 | 65 | 65 | 65 | 65 | 65 | 70 | 70 | 60 | 60 | 65 | 70 | 70 |
| Needle (clip) | X 15 (3) | X 17 (3) | X 13 (2) | X 2 (2) | X 5 (2) | X 17 (2) | X 50 (3) | X 5 (2) | X 50 (3) | X 24 (2) | X 16 (3) | X 23 (2) | X 19 (2) | X 34 (2) | X 35 (2) | X 34 (2) |
| Atomiser | 262 DG | 260 AV | 266 AV | 264 AV | 266 BN | 266 BN | 266 BN | 266 BN | 266 BN | 262 EM | 264 DG | 262 M | 262 CH | 260 CV | 260 DF | 260 CV |
| Slide | 50 | 40 | 60 | 40 | 40 | 50 | 50 | 40 | 45 | 55 | 40 | 40 | 40 | 40 | 40 | 50 |
“–” 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 idle → needle | needle position, pilot jet | 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 PHBH 26 the documented factory main jets range from 85 to 108. 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 PHBH 26
Parts that are usually replaced when overhauling this carburettor range.
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