Performance CDI for China Gas/ Grubee/ Happy Times Engine

48cc-80cc

A performance CDI optimizes the ignition timing for best engine performance, less heat, and less vibration. Many specifics determine the ideal ignition timing, including altitude, engine porting, carburetion, compression ratio, throttle habits. The "timing" is not one number though. It is a graphable curve since the correct timing changes with the changing RPM. (see graph below)

 


Jaguar Performance CDI
I got tired of the low power and vibration due to the standard CDI and so decided to do it right and install a modified motorcycle (Kawasaki KDX200) CDI and motorcycle (KX80/CR80/YZ85) high voltage coil in order to have strong ignition with timing that changes with RPM which improves spark strength for more consistent combustion (cleaner smoother running) and gives better power at all RPM and allows it to rev high without as much engine vibration or chance of knocking. (Read more about the importance of ignition timing at various RPM.)

Copy Cat Competitors
I started selling my "Jaguar CDI" in February of 2011 and now there are CDI competitors out there who say their CDIs are better than mine although theirs are mere variations of copies of my design, are not made by true engineers or technicians, and are not even bench tested to verify that they change timing with RPM (like I test mine). These people have not researched the subject at all as they do not demonstrate any depth of understanding of the topic. They just butcher my design and then promote it as being "better" than the Jaguar CDI. I'll bet they don't even know the importance of selection of charge capacitor.


Capacitors have different resistance to current spikes which affect how fast they can dump the accumulated voltage into the high voltage coil and how many years they will last. I am an electronics technician (since 1977) and understand this fine point, as well as others, and utilize an appropriately rated capacitor for performance and longevity although it costs more. If you want the original, and still the best, motorized bicycle CDI then buy my Performance CDI.

 

CDI
 

I made my own CDI unit by copying the design of the KDX200 CDI and modifying it for the Grubee engine. That, in combination with a motorcycle high voltage ignition coil, I improved the spark strength and now have an ignition system that advances and then retards the timing as revs are increased. (see video)
Stock timing is a max of 33°BTDC. (see video + graph below) The Jaguar CDI timing curve depends on the jumper settings that you select but remains similar to the KDX curve. Here is a graph comparing these CDI's: stock Grubee, Jaguar CDI, RM250:

3 CDI graphs


Here is a digital timing curve from a PLV CDI, just as an example to show that an advance/retard curve is mostly standard for 2 strokes:
Click here for more examples of timing curves.

Recently I became aware of the GP version of the RS125 with a modified intake system of a rotary valve in place of a reed valve. Unusually it had a very advanced ignition curve. Why I think it's that way is it needs to be more advanced because without the extra turbulence created by the reed valve the fuel/air mixture needs more time to fully burn. So this would apply to piston port only intakes such as what the stock Grubee engine has. So for stock Grubee engines the only downfall for the stock CDI is it's a bit weak and the timing doesn't retard past 3500 RPM. Anyway now my performance CDI allows a good amount of timing advance for piston port only intakes, as well as selectable amounts of retard for engines with reed valve. Max timing now is adjustable from 20.5°BTDC to 24°BTDC. (see graphs) In case you're wondering about how late in the RPM range the RSA125 starts to retard, that is normal for very high reving engines. Max RPM for a stock Grubee is only 6000.

Anyone after better performance usually ups the compression of the engine also. But unfortunately if you don't also increase the ignition coil voltage you could be causing more erratic running because higher compression makes it harder to consistently ignite the fuel/air mixture unless you also increase voltage available to the spark plug. Here is a graph showing the relationship. (10 bar pressure is equal to 145psi at sea level.) A 25% increase in pressure requires a 15% increase in spark voltage.

chart

How to Determine Timing: Remove the magneto cover, take the spark plug out, stick in a screwdriver to feel piston position, rotate the magnet till you find the pistons highest position, mark with a felt tip marker one of the corners of the magnet and the stator frame where the magnet corner is. That will be your TDC (top dead center) reference point. The ignition point (seen with an automotive timing light while running) on the stator frame will be a few millimeters counter-clockwise of the TDC mark which indicates the advancement of ignition before TDC. Advancing the ignition (at the CDI) more will make the magnet mark to be even more counter-clockwise than before. Use this formula to figure out how many degrees difference there is between the new position and the reference mark. Degrees=(distance between marks x 360)/(3.14 x 36.2 magnet diameter)which equates to distance between marks x 3.17
So if the marks distance is 3mm then the degree change is 9.5 degrees.

Best plug to use for standard engine: NGK BPR7HIX iridium extended tip spark plug with 13mm long thread section. This and the Denso IWF22 iridium spark plug (with removable nipple) should be gapped at .032" (.8mm) when used with my CDI. Both have a reach of 21mm from washer to end of ground electrode. For one with 19mm thread section get the BR7EIX. Best plug to use if the exhaust port has been raised and the intake port lowered for high RPM use (over 7500 RPM): NGK BPR8HIX (Denso IWF24) NGK BPR8EIX

From "Devices to improve the performance of a conventional two-stroke spark ignition engine"
+33% electrical spark power results in:
+2.5% brake thermal efficiency (engine power)
-30% carbon monoxide emissions
-38% ignition delay

Click here to read more about my CDI and how to buy it.