Air Flow and Exhaust
The key to base power in a combustion engine is managing the air flow. The components in this system must be tuned to ensure the proper air/fuel mixture.
In most stock mini-buggies and go-karts the stock air intakes and mufflers are restricting air flow and this can lead to significantly less power than the motor is capable of. Inexpensive options are available to increase your buggy’s performance.
The simplest thing to do to vastly increase the airflow is to remove the stock air intake box and replace it with a UNI Foam Filter. On a 250cc buggy, this can be clamped directly to the carburetor. On a GY6 150cc buggy, it is recommended that you use a Velocity Stack Intake (sometimes called a “Redneck Intake”), which is an approximately 6″ extension tube that attaches to the Carburetor with your UNI Filter at the other end.
Note: While it’s not absolutely necessary to use a Velocity Stack Intake on your GY6 150cc kart, it is highly recommended as the extra air travel distance decreases air volatility entering the carburetor for more consistent air/fuel mixing. Also, the engine mounting frame of some buggies and scooters may be space limited near the carburetor air intake, necessitating this extension.
Check out the BPNW How-To guide: Replacing a Stock Air Intake With a UNI Filter
In many cases, the stock carburetor on mini-buggies is perfectly functional for most purposes, even after upgrading other parts of the Air-Exhaust system. It is only at the highest ends of looking for performance gain that a larger sized carburetor may become necessary.
Stock carburetors for 250cc and GY6 150cc engines are generally in the 24mm to 28mm range depending on model and manufacturer. Performance carburetors are available in 30mm and 32mm sizes. These larger carburetors will work with both 150cc and 250cc motors, and take the 2″ intake UNI filter.
Carburetor Jets and Rejetting
Inside the carburetor, the main jet is the primary fuel delivery to the combustion chamber. The fuel is mixed with air before the resulting air/fuel vapor travels down the intake manifold into the engine.
It is of key importance for best performance to use a proper sized main jet for an optimal air/fuel mixture!
The correct size of main jet to use depends on several factors:
– Carburetor size
– Type of air intake and exhaust
– Performance cylinder head or big bore kit installed?
– Riding environment
– Altitude and ambient temperature
This can result in widely different jet sizes depending on your unique factors. Generally speaking, with just a UNI filter upgrade, you’ll need a jet somewhere between 120 and 130. If upgrading the air intake and exhaust, you’ll need between 125 and 140 and possibly larger depending on your carburetor, exhaust, and riding location (elevation above sea level).
When deciding on which jets to get for rejetting, it’s a good idea to get a range of 3-4 different sizes of jet so you can properly narrow it down to the correct size. This is not something that you want to guess on and hope it’s the right size. Use a fresh spark plug when testing each different jet size. Examining the spark plug will tell you if you are running too lean (light or no color on the spark plug end) or too rich (thick black buildup on spark plug). You’re looking for a nice caramel brown to light black color – the motor should rev smoothly through its full ramp up and not pop as it revs down. Feel free to call Buggy Parts NW if you have questions.
Information on how to change the main jet and read the spark plug can be found in the BPNW How-to guide Rejet the Carburetor: Changing the Main Jet.
These jets work on all Keihin-style carburetors used in 150cc and 250cc Mini-Buggies, Go-Karts, and many scooters using the GY6, CN250, and CFMoto 250 motors.
Since the engine is basically a mechanism for moving air through it, improving your air intake system is only half the job. What is the point of having great air inflow if the muffler is restricting the outflow?
A performance muffler opens up the airflow further and unlocks the full power of your air-exhaust system.
Buggy Parts NW offers performance exhaust solutions for most 150cc karts. The racing exhausts BPNW carries from Hammerhead Performance give a great sound and get more power out of your buggy.
Remember, every time you upgrade your air and exhaust system, you will likely have to rejet the carburetor. Click here for instructions.
More information on all these systems can be found at Buggy News – the best Mini Buggy and Go-Kart community on the Internet!