General overview of setting up the TBR7 Carburetor

 The main jet in your 2021 Tao Tao TBR7’s 30mm Mikuni clone carburetor is a critical component that controls the fuel flow for mid-to-high throttle ranges (roughly 50–100% throttle). Since you’re running a stock exhaust, foam open air cleaner, and a #22.5 pilot jet at sea level, understanding the main jet will help you optimize performance for higher RPMs and full-throttle operation. Below, I’ll break down what the main jet does, how to select the right size, and tuning tips for your setup, keeping in mind the lower precision of your clone carburetor compared to genuine Mikuni or premium brands.

What is the Main Jet?

• Function: The main jet is a small, threaded brass component with a calibrated hole, located in the carburetor’s float bowl (accessed by removing the bowl). It meters the amount of fuel drawn into the carburetor’s main circuit, which feeds the engine during mid-to-high throttle operation.
• Role in Air-Fuel Mixture: It works with the needle jet, jet needle, and throttle valve to deliver the correct air-fuel ratio (ideally ~12.5:1 to 14.7:1 for gasoline engines) at higher throttle settings. A larger main jet hole allows more fuel (richer mixture), while a smaller hole reduces fuel (leaner mixture).
• Impact: The main jet primarily affects 3/4 to full throttle. It has little influence on idle or low throttle, which are controlled by the pilot jet and fuel mixture screw (your #22.5 and current tuning focus).

Stock Main Jet for TBR7

• Typical Size: For a stock TBR7 with a 30mm Mikuni clone carb, the stock main jet is often in the #95 to #100 range (based on forums and TBR7 owner reports). However, exact sizing can vary slightly with clone carbs due to manufacturing inconsistencies.
• Your Setup: The foam open air cleaner (less restrictive than stock) increases airflow, potentially requiring a slightly larger main jet than stock to avoid a lean condition at high throttle. The stock exhaust, however, is restrictive, which may balance this out.

Choosing the Right Main Jet

Selecting the correct main jet depends on your bike’s setup, altitude (sea level for you), and performance goals. Since your carb is a clone, its less precise porting and milling may cause it to run slightly richer or leaner than a genuine Mikuni, so testing is key.

Symptoms and Jet Sizing:

• Too Lean (Main Jet Too Small):
  • Symptoms: Surging at high throttle, hesitation at wide-open throttle (WOT), engine overheating, or a white/gray spark plug.
  • Solution: Increase main jet size (e.g., from #95 to #97.5 or #100).
• Too Rich (Main Jet Too Large):
  • Symptoms: Bogging at high throttle, black smoke from exhaust, poor acceleration, or a black/sooty spark plug.
  • Solution: Decrease main jet size (e.g., from #100 to #97.5 or #95).
• Correct Mixture:
  • Symptoms: Smooth acceleration, good power at WOT, and a tan/light brown spark plug after a high-throttle run.
  • Main Jet: Likely close to stock (#95–#100) but may need slight adjustment for the open air cleaner.

Starting Point for Your TBR7:

• Recommended Main Jet: Start with a #97.5 or #100 main jet for your setup at sea level. The foam air cleaner suggests a slightly richer jet than stock (e.g., #100 over #95) to match increased airflow.
• Clone Carb Consideration: Since your carb isn’t as precisely machined, fuel flow may be less consistent. If the stock main jet (check by removing the float bowl) is #95, try a #100 and test. If it’s already #100 and running rich, drop to #97.5 or #95.

How to Tune the Main Jet

1. Check Current Jet:
   • Remove the carburetor’s float bowl (usually 4 screws).
   • Unscrew the main jet (it’s in the center, below the needle jet holder). Note its size (stamped on the jet, e.g., “95” or “100”).
2. Test Ride:
   • Warm up the engine.
   • Ride at 3/4 to full throttle on a straight stretch. Note acceleration, power, and any surging or bogging.
   • Perform a plug chop: After a WOT run, kill the engine, remove the spark plug, and check its color (tan = good, black = rich, white = lean).
3. Adjust:
   • If lean, install a larger main jet (e.g., #102.5 or #105).
   • If rich, install a smaller main jet (e.g., #92.5 or #90).
   • Change jets in small increments (2.5–5 sizes) to avoid overcorrecting.
4. Retest: Repeat the test ride and plug chop until the bike runs smoothly and the plug is tan.
5. Fine-Tune with Needle:
   • The jet needle’s clip position affects mid-throttle (1/4 to 3/4). If high-throttle is good but mid-throttle is off, adjust the needle clip (lower clip = richer, higher clip = leaner) before changing the main jet again.

Considerations for Your Clone Carb

• Quality Issues: Clone carbs can have inconsistent machining, leading to uneven fuel delivery. If tuning feels erratic (e.g., plug color varies despite jet changes), inspect the main jet, needle jet, and float bowl for debris or wear. Cleaning the carb with carb cleaner and compressed air can help.
• Float Height: Incorrect float height can mimic main jet issues (too high = rich, too low = lean). Check the float height (typically ~17–19mm for Mikuni clones; consult your manual or TBR7 forums) and adjust if needed.
• Availability: Main jets for Mikuni clones are widely available (e.g., Amazon, eBay, or motorcycle shops). Get a jet kit with sizes ranging from #90 to #110 for flexibility.

Tips for Your TBR7

• Start with #100: Given your foam air cleaner and sea-level operation, a #100 main jet is a safe starting point. If the stock jet is #95 and performance is decent, try #97.5 or #100 to compensate for increased airflow.
• Monitor Performance: If you notice bogging or poor top-end power, the clone carb’s machining might be causing fuel delivery issues. A slightly larger main jet can sometimes mask these, but cleaning or upgrading the carb may be needed long-term.
• Keep Records: Note each jet size and test result to track what works. This is especially important with clone carbs, as they can be less predictable.
• EFI Regret: While EFI is less hassle, a well-tuned carb can still deliver great performance. If the clone carb becomes too frustrating, consider upgrading to a genuine Mikuni VM26 or similar (check compatibility) for better precision.

Next Steps

• Check Your Main Jet: If you haven’t already, remove the float bowl and confirm the current main jet size. Let me know what it is, and I can suggest a specific adjustment.
• Share Symptoms: If you’re experiencing specific issues at mid-to-high throttle (e.g., bogging, surging, or poor power), describe them, and I can refine the recommendation.
• More Carb Questions: Since you plan to ask more, feel free to dive into related topics like jet needle tuning, float adjustment, or even cleaning the clone carb to improve its performance.

Let me know the current main jet size or any high-throttle symptoms, and I’ll help you nail the tuning!