Magneto question

[GWGAllisfan]

Shouldn't a magneto fire hotter the faster the RPM, or is the reverse true? I have an engine that will shock you pretty well when turned by hand, but when spun by the S/G seems to have no spark.

[D-17_Dave]

My experiance is the faster the magnetic fields pass by the coil the more juice is generated up to a certain designed point. IMO you have a partially sheared key or bad points. The only other posibility I can think of it the difference in tourqe might be rocking the cam a little to one side due to cam bearing wear or point lobe wear so the end effect is the points aren't being actuated correctly. I've had some luck by over gapping the points as needed to make the points break open cleanly so the engine will have consistant fire.

[GWGAllisfan]

That's what I thought should happen. It's a real mystery. After I left the message, I re-gapped the points, checked the armature air gap, examined the flywheel key, checked point open versus magnet position, sanded magnet area to remove rust...Still the same. I'm trying to cover every possibility before I buy a new magneto armature. The old 23D runs great on a battery coil, but I really wanted it to be back to original. Thanks for the information.

[Al]

Hi, You are correct. One thing the Rust on the magnets is an old wives tale and has no effect on the spark. This was even posted in a Briggs monthly technical bulletin. What is probably happening in this case is that the coil which is made of many probably several thousand turns of very fine wire in the secondary provides some voltage at slow speed and when the speed increases the insulation on the wires has been breached and a carbon track has developed in the coil and the voltage when it reaches a certain level "jumps across a major protion of the coil and the output drops. Sound like a bad coil to me. Al Eden

[HubbardRA]

Randy, I have had a similar problem a couple of times. In those cases it was dirty points that needed cleaning. When idleing the spark would jump off the very edge of the contact. The rest of the contact had a coating on it. It was high voltage, so you would feel a pretty good shock. The problem was that as the rpms were increased, the additional current could not be carried across the coated points, and the engine would misfire very badly, or die. Cleaning the points cured the problem. It happened to me a couple times. Run the tractor when it starts to get dark, with the cover off the points. The spark should be sharp, bright, and happening near the center of the contacts. If the spark looks weak, and is bouncing around the outer edge of the contact, then the contacts need cleaning. Buff them with sandpaper till shiny, then buff with notebook or typing paper to make sure there is no grit left on them. Check the gap and they are usually good to go.