sandt38
New member
Our machines are really fairly simple, but in some cases it would be nice to lay to rest the "is it my CDI?", "my stator?", etc. topics.
As a professional wrench with 25 years of diagnosis I have found one of the most valuable tools I have is my oscilloscope. A scope basically displays a photographic representation of electrical amplitude (voltage or peak voltage) over a period of time (frequency). Today scopes can be had on the cheap, and they can make quick work of figuring out why our machines are not functioning.
A buddy of mine had a Scrambler and his bike just quit running. His diagnosis by the manual left him questioning weather he needed a CDI or stator or ignition switch or... "Replace with a known good part" is a junk diagnosis, and it can be quite costly and time consuming. The manual was also wrong.
I brought my DVOM (no cheap meter, either it is a Fluke 87) and followed the manual. It stated the stator needed to display 33 volts peak DC current. It then stated to unplug the stator and read across the 2 wires. As a diagnostician I knew that you tested AC voltage generators this way and a DC voltage would require a voltage input which would not occur with the stator unplugged. I also knew that a stator does deliver an AC voltage. The manual also wanted me to test the pickup trigger the same way, with an expected voltage of 3.5 VDC.
In testing as the manual stated the DVOM showed 1.9VDC peak on the stator and ~0VDC on the pickup. So what did it need?
My scope showed a cranking AC voltage of 34 volts, with a clean AC signal at the stator and .9 volts (albeit a clean pattern) at the pickup. The manual stated a gap adjustment of ~.020" of the pickup relative to the flywheel... I told him I thought the adjustment was wrong. We tore it down and low and behold, the gap was ~.250. He had broken his backup pullcord starter and tied it together about 3 months ago. The knot had apparently jammed in between the pickup and the flywheel, knocking it out of adjustment. Resetting the adjustment (and cleaning up his knot) fixed the issue.
A simple $100 scope could have saved him $290 on the CDI and over $400 on the stator/pickup assy (they come as a "kit).
So, who would be interested in seeing details on how to set up a scope, analyze what you are seeing, and photographs of important testing, with known good patterns? I am planning on scoping my bike and storing the patterns (my scope costs a tiny bit more then $100 ), and frankly I will not need to photograph or write up anything on my testing, but I will take the time to help those of you interested if enough people want to see such a tutorial. I can also help analyze anomalies in the patterns you post up, if any questions are raised. If the interest is nominal I will not spend the time doing all this.
As a professional wrench with 25 years of diagnosis I have found one of the most valuable tools I have is my oscilloscope. A scope basically displays a photographic representation of electrical amplitude (voltage or peak voltage) over a period of time (frequency). Today scopes can be had on the cheap, and they can make quick work of figuring out why our machines are not functioning.
A buddy of mine had a Scrambler and his bike just quit running. His diagnosis by the manual left him questioning weather he needed a CDI or stator or ignition switch or... "Replace with a known good part" is a junk diagnosis, and it can be quite costly and time consuming. The manual was also wrong.
I brought my DVOM (no cheap meter, either it is a Fluke 87) and followed the manual. It stated the stator needed to display 33 volts peak DC current. It then stated to unplug the stator and read across the 2 wires. As a diagnostician I knew that you tested AC voltage generators this way and a DC voltage would require a voltage input which would not occur with the stator unplugged. I also knew that a stator does deliver an AC voltage. The manual also wanted me to test the pickup trigger the same way, with an expected voltage of 3.5 VDC.
In testing as the manual stated the DVOM showed 1.9VDC peak on the stator and ~0VDC on the pickup. So what did it need?
My scope showed a cranking AC voltage of 34 volts, with a clean AC signal at the stator and .9 volts (albeit a clean pattern) at the pickup. The manual stated a gap adjustment of ~.020" of the pickup relative to the flywheel... I told him I thought the adjustment was wrong. We tore it down and low and behold, the gap was ~.250. He had broken his backup pullcord starter and tied it together about 3 months ago. The knot had apparently jammed in between the pickup and the flywheel, knocking it out of adjustment. Resetting the adjustment (and cleaning up his knot) fixed the issue.
A simple $100 scope could have saved him $290 on the CDI and over $400 on the stator/pickup assy (they come as a "kit).
So, who would be interested in seeing details on how to set up a scope, analyze what you are seeing, and photographs of important testing, with known good patterns? I am planning on scoping my bike and storing the patterns (my scope costs a tiny bit more then $100 ), and frankly I will not need to photograph or write up anything on my testing, but I will take the time to help those of you interested if enough people want to see such a tutorial. I can also help analyze anomalies in the patterns you post up, if any questions are raised. If the interest is nominal I will not spend the time doing all this.
