Coleman Mini Bike Carburetor: Operation, Tuning and Upgrades

The carburetor is the key component that mixes air and fuel to be burnt in the engine. On Coleman mini bikes like the CT200U, a simple float bowl carburetor handles this vital task. In this article, we’ll take a deep dive into carb operation, tuning, troubleshooting, and performance upgrades.

How a Float Bowl Carburetor Works

Mini bikes use a basic float bowl carburetor located just before the intake manifold. Here are the key components and operation:

• Float bowl – Fuel is held in the bowl and kept at a constant level by a float that rises and falls with fuel volume. Excess flows back down to the gas tank via an overflow tube.
• Main jet – This is the primary fuel discharge port where fuel mixes with incoming airflow down the intake throat. Larger jets flow more fuel for engine modifications.
• Pilot jet – A smaller jet provides fuel at idle and low rpm operation. It has its own air supply path called the pilot circuit.
• Throttle slide – The slide raises and lowers to open and close access to the main jet. An attached needle taper alters fuel flow at midrange throttle transitions.
• Choke – The choke limits airflow to richen the mixture for easy cold starting. A separate starter jet adds extra fuel when the choke is engaged.
• Air screw – Fine tunes the air/fuel ratio specifically in the pilot circuit at idle and low throttle.

Proper float height, jetting selection, air screw adjustment, and choke operation are critical to smooth running. Regular carb inspection and tuning helps maintain optimal performance.

Symptoms of Carburetor Problems

Because the carburetor controls fuel delivery, any issue present in the carb can cause poor running or even prevent the engine from starting. Watch for these common symptoms of carb trouble:

• Difficult starting or needs repeated kicks to start when warm.
• Idle speed fluctuations or stall at idle indicating an air/fuel mixture issue.
• Sputtering acceleration or lack of full power.
• Cuts out or bogs down at high rpm indicating a fuel delivery problem.
• Excessive black smoke from rich mixture or backfiring from lean condition.
• Running inconsistently or surging.

If your mini bike exhibits any of these carb-related problems, thoroughly inspect the components and tuning as covered below. A dirty or incorrectly tuned carburetor causes the majority of performance issues.

Inspecting and Tuning the Carburetor

Here is a step-by-step guide to inspecting key components and tuning a Coleman mini bike carburetor for optimal performance:

1. Remove the carburetor from the bike to access components. Remove float bowl and inspect float height and condition.
2. Check float needle and seat for wear, debris, and proper sealing. Ensure float pivots smoothly.
3. Inspect main jet size markings. Exchange for larger jets if running engine modifications.
4. Use compressed air to blow out all fuel and debris passages including pilot jet, ports and bowl.
5. Inspect slide throttle operation and needle taper wear. Ensure full slide movement without sticking.
6. Check choke mechanism operation. Make sure the choke fully blocks airflow when engaged.
7. Adjust air screw gently to find ideal idle mixture. 1-1/2 turns out is common.
8. Set idle speed to around 1500 rpm once mixture is set. Adjust throttle stop screw as needed.
9. Ride and evaluate performance across the rpm range. Make further tuning adjustments as necessary.
10. Consider upgrading to a larger main jet and different slide needle style if still running rich or lean.

Taking the time to methodically inspect and tune the carburetor solves most running issues. Don’t hesitate to reach out to our Coleman support team if you have any tuning questions.

Carburetor Upgrades for Increased Performance

Once you move beyond basic maintenance and tuning of the stock carb, performance can be improved with targeted aftermarket upgrades:

• Larger main jets – Allow more fuel flow to match added airflow from engine build like big bore kits and exhaust. Prevents leaning out.
• Adjustable main jet carb – Allows easily fine tuning fuel delivery for any engine build without jet changes. Idle circuit is still fixed.
• New needle – Changes midrange progression compared to stock. Leaner accelerating, richer cruising.
• Choke delete – Removes unnecessary choke bulk for engine builds with easier cold starting via electric start.
• Throttle slide – Larger internal diameter improves high rpm airflow for big bore engine builds.
• Air striker – Rotating airflow control valve modifies intake velocity. Used to fine tune fuel atomization and throttle response.
• Replacement carburetor – A new performance carb like a Mikuni slides in for more tuning range. But may require fabrication.

Don’t leave a stock carburetor as the restricting factor if optimizing engine performance. A few key upgrades really optimize fuel delivery for any build level.

Carburetor Maintenance Best Practices

Like any component, proper maintenance keeps your Coleman mini bike carb operating smoothly:

• Periodically remove the bowl to clean out debris and sediment buildup. Blow passages clean.
• Lubricate the throttle shaft and choke mechanism with light oil for smooth operation.
• Inspect rubber insulators and boots. Replace any cracked pieces allowing air leaks.
• Use fuel additive to prevent corrosion and keep jets clear. Avoid gummed deposits.
• Check float level and needle condition at tune-up intervals. Replace worn parts as preventative maintenance.
• Always use new gaskets and o-rings when servicing. Don’t risk vacuum leaks from reused gaskets.
• Consider an yearly professional ultrasonic cleaning if the bike is ridden heavily or sits for long periods.

Proper carburetor maintenance and cleaning minimizes running issues and keeps your bike performing optimally season after season.

Don’t Hesitate to Rebuild or Replace

If internal components become severely worn, contaminated with grime, or physically damaged, don’t risk incorrect tuning or performance issues by working with a compromised carb. Instead, either:

A) Order a rebuild kit with all new gaskets, needle, float, jets, etc. and fully refresh the carb. Carefully inspect all passages and bores for damage during cleaning.

B) Replace with a brand new factory OEM carburetor to completely eliminate doubts about internal condition. Break-in with fresh fuel additive and filter.

Either option returns the carb to factory-fresh operation and baseline tuning. Don’t ride with a questionable carb that could leave you stranded out on the trails.

Conclusion

We hope this breakdown gives you a better understanding of how the carburetor operates on your Coleman CT200U or other mini bike model. Proper tuning and maintenance is critical for maintaining the ideal air/fuel ratio. Upgrades are also available for optimal fuel delivery when increasing displacement or airflow.

Don’t hesitate to reach out to Coleman Powersports technical support if you need any advice tuning in your particular carb. Proper jetting and adjustment makes all the difference in realizing the full performance potential of your mini bike engine. Thanks for choosing Coleman, and enjoy the ride!