Yamaha Blaster Keihin PWK28 Jetting Calculator

The Yamaha Blaster PWK28 jetting calculator provides a safe starting point for tuning a genuine Keihin 28mm PWK carburetor. Select your exhaust, airbox configuration, air filter, reeds, engine modifications, temperature and elevation to calculate a recommended main jet, pilot jet, needle and clip position.

This calculator was developed specifically for the Yamaha YFS200 Blaster using proven Ken OConnor Racing settings and jetting information from real Yamaha Blaster combinations.

The result is a starting recommendation—not guaranteed final jetting. Every two-stroke engine must be tested and tuned for its exact combination of parts, fuel, weather and operating conditions.

How to Use the Yamaha Blaster PWK28 Jetting Calculator

Select the option that most accurately describes each part of your Yamaha Blaster:

1. Choose the exhaust pipe installed on the engine.
2. Select the airbox and lid configuration.
3. Choose the type of air filter.
4. Select the reed type.
5. Choose the closest engine or porting level.
6. Identify the needle currently installed.
7. Select the current outside temperature.
8. Select your approximate elevation.

The calculator will provide recommended starting settings for:

• Keihin main jet
• Keihin pilot or slow jet
• Needle
• Needle-clip position
• Air-screw setting

Changes to the engine, intake, weather and elevation can affect different carburetor circuits. The main jet controls most of the fuel delivered at high throttle openings. The needle and clip primarily affect part-throttle operation, while the pilot jet and air screw control idle and low-throttle performance.

The calculated recommendation changes as airflow, engine modifications, temperature and elevation change.

Do not assume these exact settings will be correct for every Yamaha Blaster. Begin with the calculator’s recommendation and verify each carburetor circuit under actual operating conditions.

Understanding the PWK28 Jetting Results

Main Jet

The main jet has the greatest effect from approximately three-quarter throttle through wide-open throttle. The required size changes with the pipe, airflow, porting, temperature and elevation.

A rich main jet may cause sputtering, misfiring or an inability to pull cleanly at high RPM. A lean main jet can cause excessive heat, detonation, power loss and piston damage.

Pilot Jet

The pilot jet controls the idle and low-throttle fuel mixture. Most genuine PWK28 Yamaha Blaster combinations use a pilot in approximately the 45–50 range, although the final size depends on the engine, needle, elevation and weather.

The correct pilot should allow the engine to idle and respond cleanly with the air screw approximately one to 2.5 turns out. If the best setting is outside that range, the pilot jet may need to be changed.

JJH Needle and Clip Position

The JJH needle is the preferred starting needle for a genuine Keihin PWK28 on a Yamaha Blaster. Most combinations should begin with the clip in the second or third slot from the top.

Moving the clip downward raises the needle and richens the mixture. Moving the clip upward lowers the needle and leans the mixture.

Do not attempt to correct an unsuitable needle profile by making extreme main-jet or pilot-jet changes.

Before Jetting Your Yamaha Blaster

A carburetor cannot be properly tuned if the engine has an air leak, incorrect float level, restricted fuel flow or low compression.

Before changing jets:

• Perform a two-stroke leak-down test.
• Set the PWK28 float height correctly.
• Clean the carburetor and all passages.
• Confirm unrestricted fuel flow.
• Clean and oil the air filter.
• Inspect the intake boot and carburetor adapter.
• Use fresh fuel and a consistent premix ratio.
• Install a known-good spark plug.
• Bring the engine to operating temperature before evaluating jetting.

An air leak can make an engine appear lean regardless of the installed jet. Increasing the jet size will not repair a leaking crankshaft seal, intake boot, gasket or crankcase.

PWK28 Parts for the Yamaha Blaster

Ken OConnor Racing offers the parts needed to install and tune a genuine Keihin PWK28:

• Genuine Keihin PWK 28mm carburetor
• Keihin PWK28 Yamaha Blaster carburetor adapter
• Pro-X main jets
• The Blaster Store Yamaha Blaster parts
• Free Yamaha Blaster technical resources

This calculator is intended for a genuine 28mm Keihin PWK. Do not use these recommendations for the stock Mikuni VM26, OKO carburetors, generic PWK-style copies, Keihin PJ carburetors or larger PWK models.

Frequently Asked Questions

What is a good starting jet for a Yamaha Blaster PWK28?

A common low-elevation starting point is approximately a 160 main jet and 48 pilot with a JJH needle. The correct setting depends on the exhaust, airbox, filter, porting, temperature and elevation.

What needle should I use in a PWK28 on a Yamaha Blaster?

The JJH is the preferred starting needle for a genuine Keihin PWK28 installed on a Yamaha Blaster.

Which clip position should I use with a JJH needle?

Begin with the clip in the second or third slot from the top. The proven KOR baseline uses the second slot. Higher-flow or colder-running combinations may require the third slot.

Does elevation affect PWK28 jetting?

Yes. Air becomes less dense as elevation increases, generally requiring leaner jetting. Use the calculator’s elevation selection as a starting point and confirm the result on the engine.

Does colder weather require a larger main jet?

Usually. Cold air is denser and contains more oxygen, so the engine generally requires more fuel. Recheck the jetting when temperatures change significantly.

Can I use this calculator for an OKO or PWK-style carburetor?

No. This calculator is calibrated for a genuine Keihin 28mm PWK. Copies and oval-bored carburetors may use different slides, needles, passages and fuel-flow characteristics.

Is the calculator’s recommendation final jetting?

No. It provides a conservative starting recommendation. Final jetting must be verified on a fully warmed engine under load.