Help Understanding Oscilloscope Results (Pic's included)

[Corners]

Ok. So, I had the oscilloscope out and started playing around with trying to gather information about my bike (1 cylinder, EFI). Here's the results of the ignition timing. The blue is the crank position sensor output voltage, and the red is the primary ignition coil voltage (with a voltage divider installed). Here's some questions I have.

1) The coil dwell appears to change from idle (just over 8 ms) to some RPM's (just over 4 ms). Is that normal?
2) The trigger wheel. Results show clearly that this is a 18-2 trigger wheel, thus there is 20 degrees of crank rotation between teeth. What's not obvious is which tooth coirisponds to TDC. At idle, the factory service manual said that the timing is 10 degrees advanced. Looking at the "gap tooth" section of the graph, it looks like I may have hooked my oscilloscope up backwards. My big question is, when a tooth passes by the CKP sensor, it that supposed to produce a positive or negitive voltage? I'm wondering because I have the oscilloscope hooked up correctly according what the factory manual calls positive and negitive. If I have it backwards, everything makes sence to me because TDC would be the 3rd tooth off the gap (assuming 10 degrees TDC). I also did a few full throttle pulls, and timing appears to move 20 degress off the idle timing, which would be round 30 degrees advanced, which makes sense (stock engine tuned for 87 octane). BTW, 9k is redline.

Here's the pics. Please give me some feedback.

Idle #1


Idle #2


idle #3


Idle #4


6K RPM @ full load


7k RPM @ full load


8K RPM @ full load

[grippo]

The doubling of the dwell at low rpm is normal for non-dual spark mode, but should go away as the rpm goes up. The longer dwell won't hurt at low rpm, because what counts is the duty cycle, which remains very low at low rpm.

The polarity may be from incorrect O-scope hookup or from how the sensor is hooked up. You want to trigger on a falling edge of the wheel. This gives more accurate and more reliable timing. As the tooth approaches the sensor it will produce a rising edge, and as it goes past it will peak and fall.