waxhead
wannabe backflipper
- Location
- gold coast
The Evolution of Airbox Systems for Mikuni Carbs
Back in 2002, I decided to upgrade my ski with a pair of 44mm Mikuni carburetors. The additional power and improved throttle response were phenomenal, but the setup had a significant drawback: water ingestion. This challenge prompted me to develop a solution, leading to an innovative approach that addressed airflow and water resistance for high-performance carburetors.Early Solutions: The Adapter Plate
To mitigate water ingestion, I fabricated a plate that fit under the carb adapters. This plate allowed the use of flame arrestor adapters, effectively reducing water entry into the intake system by using the stock arrestor box. At the time, this wasn’t a common solution, but others in the community were experimenting with similar ideas. The system worked well with 38mm and 44mm carburetors, offering noticeable performance gains.The Challenge with 46mm and Greater Carbs
When transitioning to 46mm Mikunis, however, airflow issues became evident. Despite having ample airflow capacity through the flame arrestor’s 81mm intake hole—sufficient to service two 57mm carbs based on straight-line flow—performance suffered. The issue manifested as a rich condition, which could be adjusted by leaning out the mixture, but this introduced a new problem: reduced overall airflow.Diagnosing the Airflow Restriction
The restriction stemmed from how the flame arrestors were bolted to the plate. The adapters protruded into the intake hole of the stock arrestor, disrupting airflow. When we lifted the arrestor slightly, the problem disappeared, confirming that the interference was the culprit. All we had to do now was to figure out how to lift it and still have a decent way to clamp it and hold it together.Developing the Clamp System
To overcome this, we engineered a clamp system that eliminated the restriction while simplifying the installation process. The design allowed the flame arrestor to be removed with a single bolt in seconds. The carbs press against one side of the clamp, while the other side tightens securely without bending the aluminum components. This approach ensured durability and ease of use and has been running on our 8mm stroker lamey in the surf and in the river for 6 months with no issues at all.With our system, the highest point was 115mm above the top of the ski hood line. We are using an FP1 hull with a lowered hood and have never had an issue with clearance. If you are running Novis, you will find they sit lower as the tops of the carbs are machined down to make them shorter. Knowing Novis carbs are machined and JB-welded at the adapter, we now supply a small bracing arm for added stability, available for an additional $20.
Performance Benefits of the Stock Filter
Our system enabled the use of larger carbs, including 46mm Mikunis and above, with the stock filter, which remains unmatched for performance. The stock filter’s central air intake design is a key advantage. During aggressive maneuvers like end-over-end flips or rolls, water is forced to the periphery, while air remains concentrated at the center—where the intake is located. This ensures consistent airflow, even in challenging conditions.Additionally, the stock filter operates as a still airbox. Unlike open intakes that are susceptible to turbulent airflow, the still airbox ensures smooth and consistent air delivery to the carburetors. This stability simplifies tuning, provides better debris and water protection, and enhances low-end torque. Reduced intake noise is another advantage, making the system more versatile for various riding environments. It also mitigates heat soak by maintaining cooler intake air, preserving engine efficiency and reliability.
Conclusion
The clamp system revolutionized the use of flame arrestors with high-performance carburetors, addressing both airflow and water ingestion challenges. By allowing the use of the stock filter with larger carbs, it combined the best of both worlds: superior filtration and optimal airflow. This innovation underscores the importance of understanding airflow dynamics and adapting solutions to meet real-world performance needs.There’s no shortage of solutions on the market, ranging from adequate to questionable. Some designs surprisingly reduce airflow compared to stock—an odd choice that makes you wonder about the priorities during development. After all, if you’re going to compromise airflow, why upgrade at all? Flat-water riders always opt for the largest carbs they can to achieve peak throttle response and power. It only makes sense to aim for the same high level of performance in the surf.
These are being made now and will retail for $125 USD including shipping from Wax Racing Products. If you want to get in early on the pre-buy and save $25 USD, now is your chance.
