Recommended Additional Upgrades
01
Uma Laser Iridium Spark Plug
Improve ignition with Uma Racing Laser Iridium Spark Plug.
03
Uma Racing Engine Oil
Get smoother engine performance with Uma Racing Full Synthetic Engine Oil.
The UMA Racing Main Jet Kit (Set of 5) is an essential tuning tool for anyone running a PWK-style carburetor (like the UMA PWK V2 32mm, or V3 28mm). The main jet controls the fuel delivery from 50% to 100% throttle.
If your bike is “cutting out” at high speeds or failing to reach its top RPM, you likely need to swap to one of the jets in this kit to correct the Air-Fuel Ratio (AFR).
Kit Contents & Sizing
This specific set is a “Lean-to-Mid” range kit, ideal for fine-tuning 125cc to 150cc engines that are already close to their optimal settings.
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Jet Sizes included: 110, 112, 114, 116, 118
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Thread Type: Hexagonal (Large) PWK Standard
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Material: High-precision CNC Machined Brass
When to use these specific sizes?
The 110–118 range is typically used in the following scenarios:
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Standard 150cc Engines: If you have a stock R15 V2, Sniper 150, or Raider 150 with a 28mm Carb, these sizes are often the “sweet spot” for fuel economy and power.
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High Altitude Riding: If you ride in mountainous areas where the air is thin, you need smaller jets (like the 110 or 112) to prevent the engine from running too “rich.”
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Lean Tuning: If your spark plug is currently coming out black and sooty (Rich), moving down to a 114 or 116 can help clean up the combustion.
Comparison Table: Sizing Guide
| Jet Size | Effect on Engine | Best Condition |
| 110 – 112 | Leaner (Less Fuel) | Hot weather, high altitude, or stock airbox. |
| 114 – 116 | Balanced | The standard starting point for most 150cc street tunes. |
| 118 | Richer (More Fuel) | Cold weather, sea level, or high-flow open filters. |
Why choose UMA Jets over generic ones?
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Flow Accuracy: Cheap, unbranded jets often have “burrs” or inconsistent hole diameters. A generic “115” might actually flow like a “110.” UMA jets are flow-tested to ensure the number stamped on the side is 100% accurate.
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Consistent Taper: The internal taper of the jet is designed to prevent fuel turbulence, ensuring a smooth “mist” enters the engine rather than large droplets.
Tuning Pro-Tip: The “Plug Chop”
To find out which jet from this kit you need:
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Install a size (e.g., 114).
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Ride the bike at Wide Open Throttle (WOT) for about 10–15 seconds in a high gear.
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Kill the engine immediately (don’t let it idle) and check the spark plug.
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White/Grey: Too lean (Go up to 116 or 118).
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Coffee Brown: Perfect!
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Black/Oily: Too rich (Go down to 112 or 110).
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FAQs
What does the main jet control?
Main jets primarily affect higher throttle openings and full-load fueling.
Why are there 5 sizes included?
So you can test and choose the best fuel mixture for your setup.
Do I need tuning after installing exhaust/filter?
Often yes—many modified carb bikes need re-jetting for best results.
