How Do You Set Up A Nibbi Carburetor? (For A TBR7)

I finally plan to install the new Nibbi Carburetor into my TaoTao TBR7, but I wanted to review it. How do you set up a Nibbi carburetor?

Post about the unboxing the Nibbi Carburetor (PE3): TaoTao TBR7 Nibbi Carburetor, Unboxing!

My TaoTao TBR7 Nibbi Carburetor Upgrade Shopping List Post: My Nibbi PE30 Carburetor TBR7 Upgrade Shopping List.

There seem to be about five circuits on this ‘racing’ Nibbi carburetor.

1.- The Nibbi Carburetor’s Idle Circuit.

With the throttle fully closed, the air/fuel screw controls the idle. This Nibbi carburetor has an air/fuel screw, not a fuel/air screw. Learned that if the screw is on the inlet, it controls airflow into the idle circuit, and if the screw is on the outlet, it controls the fuel flow. 

This distinction is essential later since if you close the screw, depending on what type of screw it is, you can get different results since each one leans or enriches the flow differently.  

2.- The Nibbi Carburetor’s Pilot Circuit.

This circuit controls fuel/airflow into the engine from about 0% – 25% throttle open position. It is a smaller(compared to the main jet) that controls how much fuel is entrained into the air stream.

3.- The Nibbi Carburetor’s Needle Jet.

This circuit is an actual needle valve that moves up and down with the throttle position. Up to about 25%, the needle jet seems to contribute very little to the fuel flow into the air stream, which means the pilot circuit is in complete control up to 25% throttle position.

The needle is tapered after a 25% throttle open position, allowing more fuel to flow into the air stream. From about 25%-75%, the needle’s throttles fuel flow related to the carburetor’s throttle flow. 

After about 75% throttle open position, the needle valve is fully open and no longer increases fuel flow into the air stream.

Now the needle jet is adjustable, and you can position the needle up or down depending on your goal.  

If you position the needle up, it opens more and enriches the fuel more in its operating range. This is done by moving an E-clip downward, raising the need in the throttle slide.

If you position the needle down, it opens less and leans the fuel more in its operating range. This is done by moving the E-clip downward lower the needle in the throttle slide.

4.- The Nibbi Carburetor’s Main jet.

This fixed orifice controls the max fuel flow into the air stream like the pilot jet. Depending on what you read, it starts controlling or limiting about 75% throttle full open position.  

From 75% – 100% throttle position open, the main jet’s orifice controls fuel flow. The air/flow idle screw is maxed out; the pilot jet is maxed out; the needle jet is also maxed out. This means the main jet controls the upper airflow/throttle position conditions.

5.- The Nibbi Carburetor’s “Choke” Enrichment Circuit.

This “Racing” Nibbi has a different method to ‘choke’ the engine for cold startups. 

The Mikuni Carburetor I have ‘chokes’ airflow with a butterfly/choke valve. By limiting airflow, not fuel flow, the fuel/air ratio increases.

This “Racing” Nibbi Carburetor setup has an extra path for fuel to leave the fuel bowl and enter the air stream.  

When the Nibbi carburetor is in the normal operation position, the choke plunger down, the extra fuel pathway is closed off. When the choke is on, the choke plunger is up, the extra fuel pathway is open, and extra fuel flows into the engine. Found out this design is called an “enrichment circuit.”

With this out of the way, what can I adjust in the Nibbi carb to set it up for installation?

It sounds like I can adjust the air/fuel screw, the pilot circuit, the needle circuit, and the main circuit. Well went from 5 circuits down to 4; not much simplifying the Nibbi carb setup, but I’ll take it.

Side note, I plan to only do Nibbi carburetor adjustments one circuit at a time after I get the carburetor installed. Still, I have to set up the carburetor for the initial installation.

What Are The Initial Nibbi Carburetor Setup Values?

First, I will leave the needle jet at its factory-installed ‘middle’ position. There are five adjustments for the carburetor needle: two up, two down, and the middle, and I am sticking with the middle right now. That eliminates this adjustment for the initial nibbi carb setup.

Down to three Nibbi Carburetor setup adjustments.

Now the air/fuel screw. I plan to put this in the middle range of operation. About one and a half turns open. This is a standard range I have read. Not a carburetor expert, so learning as I go.

Air/fuel or fuel/air mixture screws are designed to be 1/2 to 3 turns open in their adjustment. Outside of this, you need to adjust the pilot jet size, and it’s either contributing too much or too little fuel to the idle range of the engine.  

Leaving the air/fuel screw in the mid-range position, the needle jet in its mid-position, and the choke circuit is out of my control; I am down to two initial Nibbi Carburetor setups: the pilot jet and the Main Jet.

Just two. I like this thinking of mine. 😀

Altitude And Temperature Affect Carburetors.

Temperatures will have the most significant swing with how I ride, so I will try to use my standard attribute in figuring out how to set up my Nibbi carb. I am about 400 feet above sea level. Temperatures swing as summer approaches, but I don’t feel like chasing after that variable today.

So using 400 feet above sea level as my independent variable, flashback to school days, I will research the dependent variables, the pilot jet, and main jet sizes.  

It was a pain!!!!!! It seems what works for one person, even with all factors same, altitude, air temp, fuel time, even engine, doesn’t mean you can exactly copy what works for another engine into yours. So I had found several different values from people that claim they worked in their TaoTao TBR7s and Hawk 250’s(same engine as the TBR7).  

For The Factory Setup In Nibbi Carburetor (PE30) I Received:

The factory-installed pilot jet is a size “40”.

The factory-installed pilot jet is sized “128”.

These numbers/sizes appear too large for the TBR7 at 400 feet above sea level. Using the many values, I found on the web; I decided to go with:

“38” for the pilot jet and “125” for the main jet.

Do I recommend these for you to upgrade your TaoTao TBR7 motorcycle to a “Racing” Nibbi Carburetor? Sure, why not. I bet you will be adjusting your jets later since everyone has had different results with almost every carb setup.  

Now I will get down to how you set up a Nibbi carburetor, but understand it took a while to get these fundamental setup values. A Nibbi carburetor adjustment set will be in the future trying to fine-tune the new carb to the TBR7 motorcycle.

How Do You Adjust The Pilot Jet On A Nibbi Carburetor?

• Remove The fuel bowl. 
• Remove The plastic ring.
• Unscrew the existing pilot jet you want to change.
• Screw-in, initially by hand and later carefully by flat head screwdriver, the new pilot jet.
• Reinstall the plastic ring.
• Reinstall the fuel bowl.

How Do You Adjust The Main Jet On A Nibbi Carburetor?

• Remove The fuel bowl. 
• Remove The plastic ring.
• Unscrew the existing main jet you want to change.
• Screw-in, initially by hand and later carefully by flat head screwdriver, the new main jet.
• Reinstall the plastic ring.
• Reinstall the fuel bowl.

How Do You Adjust The Main Jet On A Nibbi Carburetor?

• Using a flat-head screwdriver, close the mixture screw till lightly seated.
• Open the mixture screw; in this case, one and a half turns.

Closing statements. I am not a motorcycle mechanic, and I have never been professionally trained in the art of motorcycle maintenance. That said, if you are here, you too are not an expert and are in a quest for knowledge of how to set up a Nibbi carburetor. I hope my post explained how I concluded what I planned to set up initially on the carb and why.

I hope this helps you research and figure out what works for you. If you have a Nibbi carburetor and want feedback on your upgrade adventures, please feel free to comment below. Thank you.

In the meantime, my new “Racing” Nibbi Carburetor is set up for its installation in my TBR7 motorcycle, and I will update you guys after I am done.

Ride Safe, Ride Fun!

Extra info: https://nibbiracing.com/

---

Click To See My Recommended
TBR7 Upgrades

---

Author’s Notice: This page contains affiliate links, for which I may earn a commission by their use. Also, as an Amazon Associate, I earn from qualifying Amazon purchases.