JD Jetting provides kits and tuners for a variety of motorcycle models, with a focus on carburetor performance optimization. This article details installation procedures, troubleshooting guidance, and available tuning options based on information provided by JD Jetting. The information primarily pertains to Keihin FCR carburetors and addresses common issues such as deceleration popping and dust intrusion.
Fuel Screw Adjustment
The JDJetting fuel screw is designed to offer more precise control over the idle mixture compared to factory Keihin fuel screws. It maintains the same tolerance as original equipment. Adjusting the fuel screw impacts idle mixture control. To adjust, users may turn the fuel screw outwards in ¼ turn increments, up to one full turn, to richen the mixture. Caution is advised against excessive richening, as this can reduce fuel mileage and potentially make hot starting more difficult. If the engine requires no choke when cold starting, the idle mixture may already be on the richer side.
Power Pump Adjustment
When installing a JD Jetting kit, the power pump adjustment screw should initially be set to approximately 1 ½ turns out. Subsequent fine-tuning is recommended through riding in open areas, allowing for assessment of power delivery during throttle application. Users are advised to compare performance with the pump setting at ½ turn, 1 ½ turns, and 2 ½ turns out to determine the preferred configuration. The optimal setting varies based on riding conditions and elevation. Generally, settings further out (2 ½ turns) are more suitable for woods riding and higher elevations (above 6000ft), while settings closer in (½ to 1 ½ turns) are recommended for faster conditions with greater engine load. The goal is to eliminate any sputter or stumble when quickly opening the throttle or during gear changes.
Deceleration Popping
Deceleration popping, a common issue particularly on four-stroke engines, is often caused by an air leak at the header pipe connection to the engine. Even a small leak can induce this phenomenon, which, while generally harmless, can be disruptive. The documentation notes that as carbon builds up on the exhaust pipe, the popping may diminish over time. Some Japanese motorcycles feature a bolted header flange and gasket to prevent these leaks. Yamaha WR450 and WR250 models incorporate an air-cut coast enrichener to mitigate deceleration popping. Adjusting the jetting richer at idle can also help reduce popping in some cases. Switching to a blue-marked needle (or one step leaner) from a red-marked needle, while maintaining the same clip position, can enrich the low-end jetting without altering the mid-range.
Carburetor Vent Hose Considerations
The carburetor vent hoses are specifically routed to the float bowl chamber and not to the area above the carburetor slide. The only passage leading to above the slide is located in front of the slide itself. Installing filters on the vent hoses serves to prevent dust from entering the float bowl chamber, a function relevant when the choke is opened.
Dust Intrusion and Air Filter Maintenance
Dust intrusion into the carburetor can be a problem, even with diligent air filter maintenance. The documentation suggests that the issue may stem from the type of air filter used. Switching to the stock Honda air filter, which utilizes a finer foam, may help reduce dust ingress. Using filter skins in conjunction with the stock filter can further minimize dust passage, but may necessitate lowering the main jet by one or two steps. The documentation acknowledges that even with careful filtration, some fine particles can still pass through foam filters due to the need for adequate airflow.
EFI Tuner Functionality
JD Jetting offers EFI tuners that allow for fuel adjustments across various power ranges. These tuners do not provide specific air/fuel ratio measurements (e.g., 14:1 or 15:1). Instead, they are developed based on dynamometer testing and air/fuel measurements taken across the throttle and RPM ranges. The tuners operate within a safe fuel adjustment range, utilizing the stock EFI map as a starting point. The tuner functions similarly to having individual adjustment screws for each power range, akin to carburetor adjustments. A decal on the motorcycle references suggested dyno-tuned settings. The adjustments are intended for occasional use, similar to adjusting suspension clickers, after the optimal settings have been determined. The tuner allows users to select a power range, ride the motorcycle, and decide whether to retain the change or revert to the previous setting.
Fuel Screw vs. Leak Jet Comparison
The documentation references a comparison between stock diaphragms and a #60 leak jet versus a Honda diaphragm modification and a #40 leak jet. The choice between these configurations is described as a matter of personal preference, with performance being nearly identical based on experience. A graph illustrating accelerator pump volume versus leak jet size, using different diaphragms, is available via a provided link.
Addressing Lean Conditions
While the JD Jetting tuners do not provide precise air/fuel ratio readings, the suggested tuner settings are derived from dynamometer testing that measures air/fuel ratios across the throttle and RPM ranges. The tuners are designed to operate within a safe fuel adjustment range, building upon the existing stock EFI map. Users will recognize changes based on how the bike performs, not by a specific measurement.
Model Compatibility
JD Jetting offers jet kits for a wide range of motorcycle brands, including Beta, Gas Gas, Honda, Husaberg, Husqvarna, Kawasaki, KTM, Polaris, Rieju, Sherco, Suzuki, and TM. The documentation specifically mentions DRZ400SM and DRZ400S models.
Sources
The provided source material is insufficient to produce a 2000-word article. Below is a factual summary based on available data.