coils

[Gila Bender]

:dunno I know someone knows everything there is to know about coils, so what I need to know is can a coil check o.k. as far as primary and secondary resistance is concerned and still be bad.
Voltage at primary is battery voltage and drops about a volt and a half when cranking. Lights are brite, starter cranks fine but no spark, period. Can see spark across points when cranking. The new battery got put in with reversed polarity which caused all the trouble in the first place. It was disconnected pronto but the damage had been done. Hoping someone has a solution, my heads getting sore from beating against the garage wall.

[flash412]

To test your coil, do this...

Put a spark plug in the lead and ground it against the head, positioned with the gap where you'll be able to see the spark (if it sparks).

Remove the hot lead from the coil.

Make sure the other side has a good ground.

Take a jumper wire and connect it to the hot side of the coil.

Run the other end of the jumper to the positive battery terminal.

Every time you BREAK the circuit, a spark should jump at the plug. If it doesn't, your coil is toasted.

[Gila Bender]

:dunno Thanks, but your test of running jumper to hot side is the same as watching for spark at the points, I believe, the way this schematic shows. The Capacitor and input side of the coil forming an LC circuit on the input side of the coil. This spark does exist. The high voltage side of the coil measures about 22Kohms on a meter. With or without the spark plug there is no spark. The only way I know of that a coil can go bad is to be open and niether side is. The input side shows 1.6 ohms which I have found to be in the range of specs for replacement coils. My coil's resistance checks the same as a friends coil from an identicle bike.

[CustomSarge]

I'd swap out the capacitor, electrolytics are polarity sensitive & the reversal could've easily blown holes in the dialectric. An ohmeter test is to discharge it, & measure resistance. If good, will drop to a low resistance, but climb to infinite as the cap accumulates charge & matches the meter. Grab one about 1-4 uFd at 20+ volts if a direct replacement isn't around. I'd also consider using a 3-6Vdc separate battery source & directly fire the coil as stated earlier. Ground your forearm & hold the output in same side fingers. I'll poke you enough to know if good, but won't hurt anything. Reversal sucks, but ain't ya glad it isn't modern/computerized.

[flash412]

Originally posted by Gila Bender :dunno Thanks, but your test of running jumper to hot side is the same as watching for spark at the pointsNo, not at all. If you follow my instructions, you are disconnecting the coil from the circuit and ONLY testing the COIL (and high tension lead and spark plug cap and spark plug). The test is a PRACTICAL test, not a theoretical one. The test answers the question, "Can this coil in fact fire the spark plug at the end of it's wire?"

The Capacitor and input side of the coil forming an LC circuit on the input side of the coil.

They do form an LC circuit. But that isn't the point. The capacitor is a "condensor" that is used for an alternate path to discharge the coil primary, thus saving the points from burning.

This spark does exist.

Proving that the primary on your coil is good. Do my test to find out if the secondary is good.

The high voltage side of the coil measures about 22Kohms on a meter.

That doesn't mean that you don't have a high voltage breakdown on the secondary side. Do my test to check if the secondary is good.

With or without the spark plug there is no spark.

No spark WHEN?

The only way I know of that a coil can go bad is to be open and niether side is.

You may be about to learn something new. A HIGH VOLTAGE BREAKDOWN is not the same as open or short at low voltage.

Do you want to debate instead of running a simple two minute test?

Here's another little trouble-shooting test you can do... crank the motor with the capacitor REMOVED. If you have a bad cap, the bike WILL spark at the plugs. It will also spark like a mother at the points. So don't run it long like that or you'll soon be replacing the points.

[Gila Bender]

While I must thankyou for the simple test you suggested, I'm not sure it was worth the abuse. Who's DEBATING?


treat old people with kindness, they are only showing you what your going to be like if you should live so long!

[kbasa]

Don's old. Trust me on this one.

:p