Performance DC-CDI for GY6
This High Performance CDI is BPNW's most popular CDI. This CDI has an RPM ceiling of at least 9000RPMs. The DC-powered CDI comes in a black or yellow module.
This CDI will plug directly into your stock wiring harness. This CDI's larger physical size may necessitate relocating it elsewhere inside your electrical box.
Performance CDIs help by increasing your RPM ceiling and advancing the spark timing. Some other mods (transmission mods in particular) can increase your top speed RPMs to a point where the stock CDI will no longer rev any higher. This effectively limits your speed to whatever you're at when you hit that stock rev limit.
The performance CDI helps to recover that "lost" top end by increasing the RPM ceiling.
How to tell if you have a DC CDI:
Your CDI has two plugs, a 4-pin and a 2-pin. The 4-pin side may have 3 or 4 wires connected to it (both AC and DC versions). If the 2-pin connector has only 1 wire going to it, it's a DC CDI. If there are 2 wires attached to the 2-pin connector, then it's an AC CDI. Note: A very few DC-powered CDI systems will have two wires on the two-pin connector. For these systems, please check to see if your headlights will work while the engine is not running, and if your stock CDI has "DC" printed anywhere on it. In these cases, you need a DC CDI.
DC-powered CDI only: This CDI is adjustable!
The stock spark timing on most GY6 125cc and 150cc vehicles is ~12° before TDC. This CDI advances the base timign to 15° before TDC and allows you to adjust the timing between 15° and 20° before TDC. Simply turn the dial on the face of the CDI to make the adjustments.
The dial on this CDI will turn from around the 5 o'clock position to approximately the 7 o'clock position. At 5 o'clock it's set at 15° and at 7 o'clock it's advanced to 20°. All timing changes take effect above 3,000 RPMs, so you will likely not notice any effect on the idle speed of the vehicle.
Generally, we recommend setting it around the 12 o'clock position, but you can also try multiple settings and timed runs of a measured distance to determine the best setting for you.
More info about CDIs:
CDI's are programmed with a "map" that tells the coil to spark at a certain time in the each revolution. The CDI receives the information from the pick-up sensor down near the stator that tells it at what point in each revolution the motor currently is at.
So, for any given RPM level, the CDI knows "when" to fire the coil based on the plotting of this programmed "map".
Stock CDI's generally are only programmed with a map that goes to 5500-7000 RPMs or so (depends on model and the CDI the factory used). When you rev the engine up past this point (by modifying it in such a way as to increase the top end RPMs - like with lighter roller/slider weights), the stock CDI does not know what to do and slightly retards the timing to slow you back down until you're back on the "map".
A "No-limit" CDI is a bit of a misnomer - of course it has an upper limit programmed into it. The thing is, you're unlikely to have a transmission setup that would allow you to reach those high 10,000+ RPMs (and if you did, your engine is taking a heck of a beating on a regular basis!).
A vehicle with a CVT transmission will not continue revving up indefinitely until the motor blows up simply because you have a higher RPM limit CDI. It will increase in RPMs until the weights in the variator are fully extended and the belt is out as far as it will go (reached the max gear/pulley ratio). This is a physical ceiling to your RPMs as higher RPMs will not push the belt or weights out farther.
Lighter variator weights and heavier main torque springs will alter how high of RPMs that are required to hit this RPM ceiling, but generally speaking you have to go out of your way to reach 9-10,000 RPMs - most people will never come close to hitting that even with 10g GY6 weights or 13-15g weights in a 250cc.
That being said, the aftermarket transmission mods often easily raise your top end RPMs beyond the 5500 or so RPMs the stock CDI is mapped for. The aftermarket CDIs will allow you to rev the motor well past that point giving you the benefits of more top speed (relative to the stock CDI) and better low end power (due to the lighter weights in your tuned transmission).
Some aftermarket CDIs also come with the benefit of some timing advance. This is often built into the CDI and advances the timing curve usually around 3,000 RPMs and again later on around 7,500 or 8,000 RPMs. Many "adjustable" CDIs have this kind of auto timing advance built into them already and don't need to be manually adjusted. We generally recommend leaving these adjustable ones at the default "12:00" position unless you have a specific need for further adjustment, as the CDI has a built in advance that will accomplish timing advance without any outside interaction.