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Dellorto PHBG carburetor parts explained
A Dellorto PHBG carburetor controls the fuel and air mixture your Puch, Tomos, or other two-stroke moped needs to start, idle, accelerate, and run cleanly. The most important parts are the choke, manifold connection, float chamber, fuel hose connection, idle screw, air screw, float, float needle, main jet, choke jet, and idle jet.
In this guide, we explain what each main PHBG part does, how the jets work, how throttle position changes which fuel circuit matters most, and what to check when comparing original Dellorto PHBG carburetors with replica PHBG carburetors. The carburetor in the example photo is a 17.5 mm Dellorto PHBG replica.
What is a Dellorto PHBG carburetor?
A Dellorto PHBG carburetor is a popular carburetor for mopeds and small two-stroke engines. The carburetor mixes petrol with air before that mixture travels through the manifold into the cylinder. The better the carburetor is tuned, the better the engine starts, idles, accelerate, and responds to throttle.
PHBG carburetors are often used on tuned Puch, Tomos, and other mopeds, especially when a larger cylinder, different exhaust, or sport air filter has been fitted. A correct setup is important because the wrong fuel-air mixture can cause poor running, hesitation, flooding, four-stroking, overheating, or a dangerously lean mixture.
Parts on the outside of the PHBG carburetor
On the outside of the Dellorto PHBG carburetor, you will find the parts used for starting, mounting, fuel supply, and basic adjustment. These parts are important when you install the carburetor, connect the fuel line, set the idle, and adjust the low-rpm mixture.
Dellorto PHBG carburetor with the main outside parts marked.
| Number | Part | Function | What to check |
|---|---|---|---|
| 1 | Choke | The choke helps start a cold engine by temporarily creating a richer mixture. | Check whether your PHBG uses a manual choke or cable-operated choke. |
| 2 | Manifold connection | This is where the carburetor mounts to the intake manifold. | Check whether your carburetor slides over the manifold or uses a rubber connection. |
| 3 | Float chamber | The float chamber stores petrol for the main jet, idle jet, choke jet, and float system. | Inspect this area first if the carburetor floods, leaks, or reacts badly to throttle. |
| 4 | Fuel hose connection | This is where petrol enters the carburetor from the tank. | Check for cracks, loose fuel hose fitment, or restricted fuel flow. |
| 5 | Idle screw | The idle screw adjusts how far the slide stays open at idle. | Turning it in usually raises idle speed; turning it out lowers idle speed. |
| 6 | Air screw | The air screw fine-tunes the mixture at idle and low rpm. | Small changes can strongly affect how the engine picks up from idle. |
Parts inside the float chamber
The float chamber contains the parts that control fuel supply. If your moped idles badly, bogs, floods, leaks petrol, or does not respond properly to throttle, the float chamber is often a good place to inspect first.
The inside of the float chamber of a Dellorto PHBG carburetor.
| Number | Part | Function | What to check |
|---|---|---|---|
| 1 | Float | The float rises and falls with the petrol level inside the float chamber. | The fuel supply should shut off when the float is roughly horizontal. |
| 2 | Float needle / float pin | The float needle shuts off the fuel supply when the chamber has enough petrol. | If the rubber tip is worn or dirty, the carburetor can overflow. |
| 3 | Main jet | The main jet controls fuel supply at larger throttle openings and full throttle. | A wrong main jet can cause lean running, four-stroking, overheating, or poor pulling power. |
| 4 | Choke jet | The choke jet supplies extra fuel when starting with the choke. | On many PHBG versions, this jet is not intended to be replaced. |
| 5 | Idle jet | The idle jet controls fuel supply at idle and low rpm. | If it is dirty or incorrectly sized, the engine may stall or idle badly. |
How do the jets in a PHBG carburetor work?
The jets in a PHBG carburetor control how much petrol flows through the carburetor. The correct jet size depends on the full engine setup, including cylinder size, air filter, exhaust, ignition, carburetor size, and fuel supply.
| Part | When does it mainly work? | What can you notice with the wrong setup? |
|---|---|---|
| Idle jet | Idle and low throttle | The engine idles badly, stalls, reacts slowly to throttle, or picks up poorly from a stop. |
| Throttle slide cutaway | Low throttle and first response | The engine reacts too sharply, hesitates, or feels uneven as the throttle first opens. |
| Throttle needle and atomizer | Part throttle and acceleration | The engine hesitates, bogs, or runs too rich or too lean while accelerating. |
| Main jet | High throttle and full throttle | The engine runs too lean, gets too hot, four-strokes at full throttle, or does not pull cleanly. |
| Air screw | Fine adjustment at idle and low rpm | The engine reacts poorly to small throttle movements or does not idle smoothly. |
Interactive PHBG Tuning Simulator
Twist the throttle below to see how the specific parts of your Dellorto PHBG carburetor hand off fuel-metering responsibility to each other as throttle opening and engine load increase.
Active PHBG components
Constant systems
Original and replica Dellorto PHBG carburetors
Original Dellorto PHBG carburetors and replica PHBG carburetors are both available. A replica carburetor can work well, but there are clear differences in finish, markings, overflow connections, and small parts.
| Feature | Original Dellorto PHBG | Replica PHBG carburetor |
|---|---|---|
| Overflow connections | Original PHBG carburetors often have extra overflow connections on both sides so excess fuel can drain away neatly. | Replica carburetors do not always have these connections, or they may be made differently. |
| Logo and codes | Original carburetors are marked with Dellorto PHBG markings. Loose parts may also have an INC code or other Dellorto coding. | Replica carburetors often only show the carburetor size, for example 17.5 mm or 19 mm. |
| Finish | The casting, threads, fitment, and internal parts are usually cleaner and more consistent. | The finish can vary. Always check for dirt, burrs, thread quality, and correctly fitting jets. |
| Replacement parts | Compare codes, sizes, and markings with the old part before replacing it. | Check carefully whether jets, needles, gaskets, and float parts match your exact version. |
When should you check your PHBG carburetor?
Check your Dellorto PHBG carburetor when your moped is hard to start, idles badly, bogs, floods, leaks fuel, smokes heavily, or does not pull cleanly. The problem is often dirt, the wrong jet size, a leaking float needle, false air, or an incorrectly adjusted air screw.
| Problem | Possible cause | First thing to check |
|---|---|---|
| Moped overflows or leaks petrol | Float needle does not seal properly, float is stuck, or dirt is trapped in the seat. | Float, float needle, and fuel hose connection. |
| Moped stalls at idle | Idle jet is blocked, idle screw is incorrectly adjusted, or the engine is drawing false air. | Idle jet, air screw, intake manifold, and gaskets. |
| Moped bogs at full throttle | Main jet is too small, fuel supply is restricted, or the air filter/exhaust setup is not matched properly. | Main jet, fuel flow, air filter, and exhaust setup. |
| Moped four-strokes or smokes heavily when accelerating | Mixture is too rich, main jet is too large, or the choke is sticking. | Main jet, choke, throttle needle, and air filter. |
| Moped picks up poorly from low rpm | Air screw, idle jet, or throttle needle is not adjusted correctly. | Air screw setting, idle jet, and throttle needle clip position. |
Basic order for tuning a PHBG carburetor
Tuning a PHBG carburetor works best when you follow a clear order. Do not change everything at once. Check the basics first and adjust step by step.
Work calmly and logically. Carburetor tuning is a combination of jet size, air supply, fuel supply, ignition, exhaust, and the complete engine setup.
Back to topShop PHBG setup parts at Puchshop
When you tune or rebuild a PHBG carburetor, it helps to have the correct jets, seals, manifold parts, fuel hose, and air filter parts available before you start. Use the table below to jump to the most relevant Puchshop categories.
| Setup area | Useful when | Shop |
|---|---|---|
| Dellorto PHBG parts | You need replacement PHBG parts, seals, needles, or small carburetor parts. | Shop PHBG parts |
| Jets | You are tuning the main jet or idle jet after changing cylinder, exhaust, or air filter. | Shop jets |
| Manifolds | You are mounting a PHBG to a different intake setup or checking for false air. | Shop manifolds |
| Air filters | You changed the air intake and need to retune the carburetor safely. | Shop air filters |
Need parts for your Dellorto PHBG setup?
Find PHBG replacement parts, jets, manifolds, and setup parts for your Puch moped at Puchshop.
Shop Dellorto PHBG parts Tip: change one tuning part at a time and test before making the next adjustment.FAQ: Dellorto PHBG carburetor parts
What does the main jet do in a Dellorto PHBG carburetor?
The main jet controls how much petrol the engine receives at high throttle openings and full throttle. A main jet that is too small can make the engine run lean. A main jet that is too large can cause four-stroking, poor pulling power, or a rich mixture.
What does the idle jet do?
The idle jet controls the fuel supply at idle and low rpm. If this jet is dirty or does not match your setup, the moped can idle badly, stall, or pick up poorly from low rpm.
What is the air screw for on a PHBG carburetor?
The air screw is used for fine adjustment of the mixture at idle and low rpm. Small changes to the air screw can strongly affect how the engine picks up from idle.
What is the difference between an original and replica Dellorto PHBG?
An original Dellorto PHBG usually has better finish, original markings, Dellorto logos, and sometimes extra overflow connections. A replica PHBG can work well, but always check the finish, jets, markings, and fitment carefully.
How do I know if my float closes properly?
The float should shut off the fuel supply when it is roughly horizontal. If the carburetor overflows or fuel keeps leaking, the float needle may be dirty, worn, or incorrectly installed.
Can I use a cable-operated choke on a Dellorto PHBG?
Yes, many PHBG carburetors can use a cable-operated choke. This allows you to operate the choke with a cable, for example from the handlebar. Always check whether the choke fits your specific PHBG version.
