Pamco ignition? Crazy backfire!

[mlucio]

Ok, so the other day I went to take my bike out. It was running fine, I went to fill up and and continue my ride. With a full tank of gas, about a thousand feet away from the station, my bike just shuts off. I've notices a slight issue with my gass cap, it's vented, but not venting properly. So I figured I had some vaccum seal/vapor lock issue. I'm sitting there trying to kick it over for about 10 minutes, a few times with the cap off and on, and nothing. So I call for a ride home, I move my bike over to a new spot in the lot I died in, and turn the key on on my bike, and the mother of all backfires pop off. Literally sounded like a canon was shot off next to my head. I get the bike home with my dad, unload it and that's the last time I've seen the bike. I've been away since then. So bear with me because I don't have direct access to the bike at the monent. But he called and said there was no spark anymore, and then called again and said theres voltage coming through the coil.

My question to you all is, if anyone's run into a similar problem, can you shoot me in the right direct of where to start locating the problem.

Thanks ahead of time for any info everyone!

 

[pamcopete]

Try this procedure:

Testing the coil:

1. Using the lowest scale on the meter, measure the resistance between the primary terminals with the wires removed. Should read from 2.5 to 4.5 Ohms.
2. Using the highest scale on the meter, measure between one of the primary terminals and the center core of the coil. Should be infinite resistance. (open)
3. Measure between one of the primary terminals and one of the plug wire terminals. Should be infinite resistance. (open circuit)
4. Measure between one of the plug wire terminals and the core of the coil. Should be infinite resistance (open circuit)
5. Measure from one plug terminal to the other. Should be 15,000 to 20,000 Ohms

Testing the PAMCO

1. Use a voltmeter and check for battery voltage on each of the red/white wires with the key and kill switch are turned on.
2. The dual output coil has to have both spark plug wires connected to a spark plug at all times.
3. To test for spark, connect one of the spark plug wires to a spark plug that is grounded to the engine.

To test for spark without having to turn the engine over, do this procedure:
1. Remove the PAMCO rotor.
2. Remove the locating pin in the advance rod.
3. Reinstall the rotor, but without the pin.
4. Replace the nut holding the rotor on loosely. This will allow you to spin the rotor to produce a spark without having to turn the engine over.
5. Connect one of the spark plug wires to a spark plug that is grounded to the engine, but not installed in the engine.
6. Make sure that the other spark plug wire is connected to a spark plug in the engine.
7. Turn on the ignition switch and the kill switch.
8. Spin the rotor while looking at the gap in the spark plug for a spark.
9. Turn off the kill switch and the ignition switch.

 

[mlucio]

Awesome! Thanks a lot! You're the man Pete.

 

[mlucio]

Ok, quick question about that first procedure. Step 2 says, "measure between one of the primary terminals and the center of the coil", would that be power into the coil and ground? If so I got a reading on my meter of O.L. I can't remember of that would be infinite or not.

 

[Marvelicious]

Open loop = infinite

 

[mlucio]

There's one other thing I guess I should mention. The reason it backfired I guess. Every once and a while when I simply turn the key on, it's like the compression left in the motor is released through the exhaust. Because when I turn my key on the coil is instantly energized and it must ignite whatever's left in the motor. Idk what the hell is going on with that but I believe that's what's causing this entire issue.

 

[pamcopete]

mlcio,

The center of the coil is the laminated metal core which is not connected to anything. The test is to be sure that the windings are not shorted to the core.

When you turn the ignition off, it may produce a spark and if there is any residual fuel mixture in the cylinders that will cause a backfire. Normally, one does not turn the key off with the engine not running. If you are going to do some other electrical work on the bike, then turn off the kill switch so there is no power going to the ignition.

 

[mlucio]

Yeah, I'm just baffled now. All my readings matched the procedures you mentioned. But just can't get a spark, plugs are fine too, ran them in a different motor and were good. I'm just startin to lose my mind now.

Are there any other reasons reported for no spark?

 

[Tomterrific]

Check that a carb didn't blow off.

If you have a Pamco and a plug wire is off you cannot turn the ignition OFF because that will fire the coil and blow out the power transistor. This is only a problem if the secondary of the coil is not able to discharge/spark to ground. Of course if one is to never turn the key on while they are working with ignition parts everything is okay. Think back and see if this is a possibility.

I've replaced power transistors but I don't know what the Pamco takes or if mere mortals can get one. DIYEFI has Bosch ignition transistors.

 

[mlucio]

I think I understand that, is there a way to test those? Just check the continuity across them or something like that?

 

[Tomterrific]

I'm sorry, I don't know how to test these.

 

[pamcopete]

Check that a carb didn't blow off.

If you have a Pamco and a plug wire is off you cannot turn the ignition OFF because that will fire the coil and blow out the power transistor.

This is only true with the "Green Monster" coil, although it is never a good idea to run an electronic ignition with one plug disconnected.

Page 150 of the Haynes manual has this to say about that with the factory TCI system:

"Note: On no account run the engine with the sparking plug cap(s) removed. Due to the high secondary voltage, it is possible to damage the internal insulation of the secondary coil."

Here is a video of the PAMCO driving a 17-6903 "Ultimate" coil with one spark plug disconnected.

No damage was done to either the PAMCO or the coil.

 

[pamcopete]

Yeah, I'm just baffled now. All my readings matched the procedures you mentioned. But just can't get a spark, plugs are fine too, ran them in a different motor and were good. I'm just startin to lose my mind now.

Are there any other reasons reported for no spark?

Did you try spinning the PAMCO rotor with the locating pin removed?

 

[Tomterrific]

That is true. No transistorised ignition should be operated with a plug wire removed. The Pamco isn't being singled out. Then again, the old analogue Boyer owners still balance carbs by pulling off a plug wire. I can only speculate how the Boyer gets away with that.

Some coils are made with a safety gap to jump secondary to ground if the plug wire is off. Is there a tick-tick of spark in that video? I can't watch it on my old diesel fired computer. Remember Mr Riggs GM module with GM coil ignition? He ran with a plug wire off and it jumped a spark about 6" to get to ground and ran on one cylinder!!! 8^o I have been using the pull a plug wire and balance the carbs method on my Triumph and XS650 for a very long time and the coils are original on both. Weak coils is my take on why they last and I have points which are much like rocks. So many coils don't instantly blow out but transistors can.

I still think the power transistor (ignitor) is suspect in any case where an owner attempted to work on a transistorised ignition. Very easy to screw up so some thing to keep in mind.

 

[mlucio]

Pete, I hadn't tried removing the locating pin until now, I was just using the kickstarter all day. Idk what the fuck just happened but it's all like nothing ever happened.
Thanks to everyone who helped, this place rules!

 

[pamcopete]

That is true. No transistorised ignition should be operated with a plug wire removed. The Pamco isn't being singled out. Then again, the old analogue Boyer owners still balance carbs by pulling off a plug wire. I can only speculate how the Boyer gets away with that.

I have been using the pull a plug wire and balance the carbs method on my Triumph and XS650 for a very long time and the coils are original on both. Weak coils is my take on why they last and I have points which are much like rocks. So many coils don't instantly blow out but transistors can.

I still think the power transistor (ignitor) is suspect in any case where an owner attempted to work on a transistorised ignition. Very easy to screw up so some thing to keep in mind.

Tom, the difference here is that your Triumph and XS650 points models do not have a dual output coil, so the secondary is internally connected to the primary terminals. The battery terminal on the coil is equivalent to ground as it is only 12 volts above ground, so the high voltage secondary has a path to get to the other end of the high voltage winding.

In the case of a dual output coil, there is no such path, so the high voltage on the spark plug that is connected goes across the spark plug gap, to ground and then to one of the primary terminals and back to the secondary except that there is no path for the current, so it makes a path through the insulation, frying the insulation in the process.

A well made coil, such as the 17-6903 "Ultimate" coil, has very high dielectric strength in its insulation, so the only path for the errant current is through the capacitance between the windings which does not cause any damage. You will note from my video that the result is a very weak spark that would screw up your attempts to sync the carbs using the dead cylinder method with one plug disconnected.

 

[Tomterrific]

Thanks for the coil school Pete. I now understand better the differences in why a dual outlet coil is at more risk than a single outlet coil, The old Boyers use two 6v coils wired in series so this must explain how the owners can get away with pulling a plug. I figured this was the reason but now I understand it a little better.

When the high voltage of the secondary goes to the primary terminal, is this why a power transistor fails on electronic ignition?

 

[pamcopete]

Tom,

In the failures that I have observed on my test setup, the errant high voltage shorts out the primary winding on its way to the secondary so there is a short between the +12 from the battery and the collector of the transistor. This creates a very high current that exceeds the maximum design capability of the transistor so it instantly fries. In fact the instant heat generated is so intense that the transistor actually pops open. All of this happens so fast that the fuse does not have time to react.

Just having the high voltage return to the secondary via the primary winding would not cause a problem because that is the way a single output coil works and the PAMCO is used in the 277 rephase ignition to drive a single output coil with no problem.

 

[mlucio]

Do those instructions for testing the coil apply for the single output coils for a rephased engine??

 

[pamcopete]

mlicio,

With one exception. As discussed above, a single output coil has the secondary internally connected to the primary, so you will read the secondary resistance between the only plug wire and either of the primary terminals. Either primary terminal will read the same resistance to the plug wire because the primary resistance is so low compared to the secondary resistance that the difference is not readable.