Puch tuning! Which carburetor for 50cc, 70cc and 74cc cylinders?

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Which carburettor does my Puch need?

Choosing the correct Puch carburettor is one of the most important steps when tuning a Puch engine. The right carburettor size improves throttle response, acceleration, fuel mixture, and engine reliability. The wrong size can make your moped harder to tune, slower off the line, or unsafe if the mixture runs too lean.

For most Puch street setups, the best carburettor is usually a 12mm or 15mm Bing for a standard 50cc engine, a 15mm Bing or 17.5mm Dellorto for a fast 50cc or 70cc setup, and a 17.5mm, 19mm, or 21mm carburettor for a properly modified 74cc or race engine.

Quick answer: A bigger carburettor does not automatically make a Puch faster. The carburettor must match the cylinder, intake manifold, exhaust, ignition timing, crankcase flow, and the way the engine is used. For most daily and street builds, a 15mm Bing or 17.5mm Dellorto is the best balance between performance and easy tuning.

Quick overview: which carburettor for which Puch cylinder?

Use this table as a practical starting point. Final jetting always depends on your cylinder, exhaust, air filter, intake, ignition, fuel supply, and local riding conditions.

Engine setup	Recommended carburettor size	Best use	Important note
Standard 50cc Puch	12mm or 15mm Bing	Reliable street riding	Easy to tune and good for daily use.
Fast 50cc Puch	15mm Bing or 17.5mm Dellorto	Sporty street setup	Works best with improved exhaust and intake flow.
70cc Puch	15mm Bing or 17.5mm Dellorto PHBG	Strong street or light performance setup	17.5mm is usually the practical maximum for many normal 70cc builds.
74cc Puch	17.5mm, 19mm, or 21mm	Performance or race setup	Larger sizes only work properly when intake, exhaust, and engine cases support the airflow.
Reed-valve or modified race engine	19mm or 21mm	High-rpm racing	Requires careful tuning, correct jets, and a complete matching setup.

Order your Puch carburettor, intake parts, and main jets at PuchShop before you start tuning.

How a Puch carburettor works

A carburettor mixes air and fuel before the mixture enters the engine. For a two-stroke Puch engine to run well, the mixture must be rich enough to cool and protect the cylinder, but clean enough to accelerate smoothly without drowning the engine in fuel.

What happens inside the carburettor?

Air flows through the carburettor venturi.
The air speeds up and creates a pressure difference.
Fuel is drawn from the float bowl into the airflow.
The throttle slide controls how much air enters the engine.
The main jet, needle, idle jet, and air screw control fuel delivery at different throttle positions.

A correctly working carburettor gives the engine a stable fuel mixture from idle to full throttle. That is why carburettor condition and tuning are just as important as carburettor size.

Why carburettor size matters on a Puch

Carburettor size must match the airflow demand of the engine. A bigger carburettor can support more power, but only when the cylinder, intake manifold, crankcases, exhaust, and ignition are also prepared for that extra airflow.

Carburettor situation	What happens	Typical result
Carburettor too small	The engine cannot breathe enough at higher rpm.	Limited top-end power.
Carburettor correctly sized	Air speed and fuel mixture stay balanced.	Good throttle response, acceleration, and reliability.
Carburettor too large	Air speed drops and fuel delivery becomes harder to control.	Weak low-end response, difficult jetting, and higher fuel use.

Signs that the carburettor is too large

The moped feels lazy when you open the throttle.
The engine bogs before it starts pulling.
Jetting changes do not give a clean result.
Fuel consumption increases without a clear performance gain.

Signs that the carburettor size is correct

The engine responds cleanly when you open the throttle.
Acceleration is smooth through the rev range.
The spark plug colour stays safe after test riding.
The engine feels strong without becoming hard to tune.

Which carburettor for a standard 50cc Puch?

A standard 50cc Puch engine usually works best with a Bing carburettor. This setup is reliable, easy to tune, and strong enough for normal street riding.

Carburettor	Best for	Why it works
12mm Bing	Original or low-speed 50cc street setups	Reliable, smooth, fuel efficient, and easy to tune.
15mm Bing	Stock or lightly tuned 50cc Puch engines	Better acceleration and throttle response while still being simple to tune.

For many riders, the 15mm Bing is one of the best upgrades for a stock or lightly tuned Puch. It gives the engine more breathing room without making the setup too aggressive.

Street setup tip: Do not choose a huge carburettor for a normal 50cc cylinder. A well-tuned 15mm Bing will usually ride better than an oversized carburettor that does not match the rest of the engine.

Which carburettor for a fast 50cc Puch?

A performance 50cc cylinder can use more air and fuel than a standard cylinder. The correct carburettor depends on the cylinder type, exhaust, intake, and how high the engine is designed to rev.

15mm Bing: best for most fast street setups.
17.5mm Dellorto: a good choice when the intake and exhaust are also upgraded.

Correct jetting is more important than simply fitting a larger carburettor. A well-tuned smaller carburettor often performs better than a poorly tuned larger one.

Which carburettor for a 70cc Puch?

A 70cc Puch engine needs more airflow than a 50cc engine, but it still needs a balanced carburettor size. For most street builds, a 15mm Bing or 17.5mm Dellorto PHBG is the best starting point.

15mm Bing: excellent for street riding, strong response, and simple tuning.
17.5mm Dellorto PHBG: ideal for performance street setups with a better exhaust and intake.

When should you use a 19mm or 21mm on a 70cc Puch?

A 19mm or 21mm carburettor can work on a 70cc Puch, but only when the engine is built to use the extra airflow. That normally means:

Reed-valve intake
Enlarged intake manifold
Modified crankcases
Performance exhaust
Correct ignition timing

On a normal 70cc street setup, 17.5mm is usually the practical maximum.

Which carburettor for a 74cc Puch?

A 74cc Puch engine can benefit from a larger carburettor, but the best choice depends heavily on the complete engine build.

Carburettor size	Best use	Important note
17.5mm	Mild 74cc street builds	Good balance of response, tuning, and reliability.
19mm	Stronger performance setups	Works best with better intake and exhaust flow.
21mm	Race-style engines	Needs correct intake, exhaust, ignition, and crankcase work.

Popular choices for 74cc Puch engines include Dellorto PHBG carburettors and Polini CP carburettors. A 74cc engine with a restricted intake or mild exhaust will not automatically perform better with a 21mm carburettor. The full setup needs to work together.

When does a big carburettor work on a Puch?

A big carburettor works when the engine can actually move more air. This usually means the engine has been modified beyond a basic cylinder and exhaust upgrade.

Important tuning warning: Do not fit a large carburettor and assume the engine is safe. A two-stroke engine that runs too lean can overheat and damage the piston, cylinder, or crankshaft. Always start rich, test carefully, and adjust step by step.

Bing vs Dellorto vs Polini carburettors for Puch

Bing, Dellorto, and Polini carburettors can all work well on a Puch, but they suit different types of builds.

Carburettor type	Best for	Main advantage	Typical Puch setup
Bing	Standard and street engines	Reliable, simple, and easy to tune	50cc, fast 50cc, mild 70cc
Dellorto	Performance street and race engines	More tuning options and strong parts availability	Fast 50cc, 70cc, 74cc
Polini CP	Compact performance and race builds	Strong flow in a compact carburettor body	Modified 70cc, 74cc, race setups

Bing carburettors

Best for standard and street engines.
Easy to tune.
Reliable and consistent.
Great choice for riders who want simple performance.

Dellorto carburettors

More tuning options.
Good choice for performance cylinders.
Widely used in racing and tuning setups.
Works well when matched with the correct intake and exhaust.

Polini CP carburettors

Compact design.
Strong performance potential.
Good for race-style setups.
Best when the engine is already modified for more airflow.

For most Puch riders, the 15mm Bing remains one of the best all-round carburettor choices. For stronger performance builds, a 17.5mm Dellorto PHBG is often the next logical step.

Basic Puch carburettor tuning

Carburettor tuning decides how the engine feels and how safely it runs. Even the best carburettor will perform badly if the jetting is wrong.

Main carburettor tuning parts

Part	What it controls	When it matters most
Main jet	Fuel delivery at wide-open throttle	Full throttle and high rpm
Needle	Fuel delivery in the middle throttle range	Acceleration and cruising
Idle jet	Low-speed fuel delivery	Starting, idle, and small throttle openings
Air screw	Fine adjustment of idle and low-speed mixture	Idle quality and first throttle response
Float height	Fuel level inside the float bowl	Stable fuel supply and flooding prevention

Need to tune your setup? Start with the correct Puch main jets and make small changes one step at a time.

Common Puch carburettor problems

Many carburettor problems come from incorrect jetting, dirt in the carburettor, worn parts, air leaks, or a carburettor that is too large for the engine setup.

Problem	Possible cause	What to check
Engine floods	Too much fuel, leaking float needle, incorrect float height, or jetting too rich	Float needle, float level, main jet, choke, spark plug
Engine runs lean	Not enough fuel, air leak, main jet too small, or restricted fuel flow	Main jet, intake leaks, fuel tap, fuel hose, carburettor gasket
Engine bogs when opening throttle	Carburettor too large, wrong needle position, or mixture too rich/lean	Needle, main jet, carburettor size, air filter
Engine only runs with choke	Lean mixture or blocked idle circuit	Idle jet, air leaks, carburettor cleaning, intake gasket
Poor full-throttle performance	Wrong main jet, restricted fuel flow, or mismatched exhaust/carburettor setup	Main jet, fuel supply, exhaust, spark plug colour

Lean mixture warning: A lean two-stroke engine can overheat quickly. If your Puch gets hot, loses power, or the spark plug looks too light after a full-throttle test, stop riding and check the jetting before continuing.

Conclusion: which carburettor should you choose for your Puch?

The best carburettor for your Puch depends on the complete engine setup. For most street mopeds, a 15mm Bing or 17.5mm Dellorto is the best balance between performance, throttle response, reliability, and simple tuning.

Use a 12mm or 15mm Bing for a standard 50cc Puch.
Use a 15mm Bing or 17.5mm Dellorto for a fast 50cc setup.
Use a 15mm Bing or 17.5mm Dellorto PHBG for most 70cc street setups.
Use a 17.5mm, 19mm, or 21mm for a 74cc or modified race engine.
Only use a large carburettor when the intake, cylinder, exhaust, and crankcases can support the airflow.

Choose the right carburettor, install the correct jets, and tune carefully. That is the best way to get more performance from your Puch without sacrificing reliability.

FAQ: Which carburettor for a Puch?

Can I use a 21mm carburettor on a 50cc Puch?

Only if the engine is heavily modified with a reed valve, upgraded intake, modified crankcases, and a tuned exhaust. On a normal 50cc Puch, a 21mm carburettor is usually too large.

Is a 15mm Bing good for a 70cc Puch?

Yes. A 15mm Bing works very well for most 70cc street setups. It gives strong throttle response, good reliability, and easier tuning than a larger carburettor.

What is the biggest carburettor for a normal 70cc Puch?

A 17.5mm carburettor is usually the practical maximum for a normal 70cc Puch. Larger carburettors often need a reed-valve intake, modified crankcases, and a performance exhaust to work properly.

Does a bigger carburettor make more power?

Only if the engine setup supports more airflow. Without the correct cylinder, intake, exhaust, and tuning, a bigger carburettor can reduce throttle response and make the engine harder to tune.

When do I need a 19mm or 21mm carburettor?

You need a 19mm or 21mm carburettor for race engines or heavily modified setups with upgraded intake systems, modified crankcases, performance exhausts, and correct ignition timing.

What is better for a street Puch, Bing or Dellorto?

For a simple street Puch, a Bing carburettor is usually easier to tune and very reliable. For a stronger performance setup, a Dellorto PHBG gives more tuning options.

Do I need to change the main jet after fitting a new carburettor?

Yes. Whenever you change the carburettor, cylinder, exhaust, air filter, or intake, you should check and adjust the main jet. Start safely rich and test carefully.