Iím interested in trying to determine the baseline performance of my magneto using the ď1156 Bulb TestĒ.
I performed this test last night, as described in this procedure: http://www.mtfca.com/discus/messages/708324/MAGNETO_TEST-760271.pdf
At engine idle, I had a healthy 8-9 volts and the bulb was bright.
At moderate throttle, I had around 15 volts and the bulb was very bright.
The problems and questions come at determining the output at high engine speed. I could goose the throttle to obtain high RPMs, but I was uncomfortable holding it there to get an accurate measurement. The sound and vibration of the engine under high RPM when the car is stationary is like a singer sowing machine ready to come apart! Iím using a Simpson 260 and the sweep of my needle seems to lag behind the RPMs and move slow. So by the time I goosed the throttle and then backed off, the needle was already falling. I managed to get it up to around 17-19 volts and the bulb was very very bright, but it was momentary.
1. Does the bulb need to be connected directly to the magneto post to get an accurate measurement? Does the ground connection need to be close to the post as well? I connected the bulb to the red lead at the firewall terminal block and the other to the ground screw on the horn. I connected the meter at the same points.
2. Should I try with a more responsive (faster) meter or are they all the same? This is just my lack of experience with analog meters.
3. Is the high (engine) speed measurement taken while goosing the throttle or opening the throttle and holding it there? Seems very hard on the engine, but again maybe Iím showing my in experience.
Any thoughts on the measurements I posted above? My car idles great and runs great on magneto. The primary reason Iím going down this path is because my car does not start on mag. Iím trying to rule out the magneto (which was rebuilt, magnets charged), before moving to the coils which are a complete unknown.
Perhaps your chasing the wrong thing?
Give me a call and I can help. I can talk faster on the phone than type on this damn computer.
I have noticed most of those bulbs blow at 18 volts.
That is usually good enough to run on Mag.
Keep a supply of bulbs on hand if you plan to do that test on a good Mag.
Or you could test the output of the magneto this way:
Update: Since these posts live on forever and end up being referenced by folks trying to figure out their own issues, I thought I would provide an update. I took Ron up on his offer to help me sort out what was going on with the car. What I learned in subsequent conversations is that the 1156 bulb test is really an approximation method which infers proper magneto operation, in lieu of actually measuring the output with a calibrated meter. So, in short, I was really overthinking this test with my questions above. The bottom line is that my magneto seemed to be operating satisfactorily based on observations conducted during the test as prescribed. After ruling out a few other things, the coils became suspect since I had no knowledge of their history prior to installing them in the car. I took this as an opportunity to get them properly rebuilt and adjusted by Ron (something I had planned to eventually do), and oh my, what a difference in how the car runs. I was even able to start the car under magneto power with one swift pull of the hand crank which was the reason I had looked into all of this, despite the car always starting easily on battery.
Having reliable, properly functioning components is important. But understanding the basics of magneto operation may be even more so. I now have a better running car and learned a bit in the process. Another thanks to Ron and this forum which continues to be a source of help in times of trouble.
Dan, Best engine ignition performance possible is achieved with coils adjusted for equal and consistent firing Time.
There are other variables that effect engine ignition performance that also must be properly adjusted and functioning like spark plug gap and timer. Any variation in coil activation due to timer contact resistance, bounce or skip will produce cylinder to cylinder timing variation and degrade engine performance and smoothness.
There was a Time when I cared, but not anymore.