Re: Testing coil with a 9v, How?
Re: Checking a mag coil with a 9 volt<br /><br />Here's a small engine trick I learned long ago for checking a mag coil while still on the engine. Use at your own risk. I'm not responsible for misuse of this technique resulting in damage/injury/yada yada yada. I assume that you have the magneto ignition with two independent circuits and coils.<br /><br />1) Open the points corresponding to the coil you wish to test, and hold them open with a thin insulator, or rotate the crank until the point cam holds the points open. Turn the ignition on or disconnect the p-leads (those black wires that connect the points to the blue and white wires at the terminal block).<br /><br />2) Connect the plug wire to a known-good sparkplug and ground the base of the plug so you can observe the spark (or setup however you regularly check for spark).<br /><br />3) Connect one terminal of a ***9-volt*** battery to ground. I use a 9-volt battery connector salvaged from some old electronics with a small alligator clip soldered on.<br /><br />4) Briefly touch (a fraction of a second is plenty) the other terminal of the battery to the moving point contact or the screw terminal where.<br /><br />5) A nice blue spark should jump the spark gap when you release the momentary connection made in step 4. You will also very likely get a smaller spark at the battery lead.<br /><br />In normal operation, passage of the magnet in the flywheel past the stator induces a current in the primary windings. What you are doing is supplying that current from a battery instead. When you "break" that battery contact, you perform the same fuction as the breaker points opening.<br /><br />Some additional warnings:<br /><br />Do NOT use the 12-volt starting battery to perform this test. Doing so may very well overheat and destroy the coil. A small alkaline battery is current-limited, but a large lead-acid battery can easily sink enough current to melt the coil. In fact, it sounds like that high current may well have destroyed the coil in the first place.<br /><br />This test will not work if the points are closed. Be sure they are open and that you don't have any other loose or worn wires that can cause a short. Make sure the ignition switch is turned on and working correctly. Otherwise pull either the white or blue wire from the terminal block to ensure the points aren't grounded.<br /><br />This test will not work if the condenser is shorted. Be sure you have a good one, or remove it from the circuit.<br /><br />This is not a valid test for spark strength. It works fine for me with a sparkplug. It might not work with a spark tester, nor should it used be a basis for determining coil strength.<br /><br />Re: Coil sources<br /><br />I just received a good coil from Lou's Outboard Service in Duncansville, PA (814-695-6562) for less than $75 shipped. Assuming your magneto is like the one on my '65 45 HP model (see pic below), and not the circular type with 8 coils spaced around it, he should have a few left. If not, I am getting a pile of parts salvaged from a running powerhead in a week, and would be willing to sell one of the coils.<br /><br />
<br /><br />Cheers,<br />Matt
