No spark

[spivey]

Lets start this discussion by saying I hate mysteries. I have just done a complete rebuild on all 4 carbs on my 78E. I had the carbs pretty close to being sync'd when I had to leave town for a couple of weeks.
Got home last week fired up the bike and it ran like crap. It would stutter,stumble,backfire. No matter what I did with the sync it wouldn't clear up. Finally it just died. First I checked that fuel was getting to the carbs which it was. Air filter isn't installed yet so its not starving for air. So Ive moved on to the electrics. Here's what Ive checked so far.
1 battery voltage. Its a little low @ 10.95v. Still strong enough to spin the motor.
2 voltage to the coils is 10.95
3 primary coil resistance is 3.3 ohms right side,3.4 ohms left side. The coils are Accell super coils with Pro 9 wires
4 secondary coil resistance is 28.2k ohms right side, 49.5k ohms left side.
5 checked all four wires going to the pickups on the vac. advance. I toned them with my multimeter from end to end, no breaks in the wiring.
6 checked emergency shut off switch, it works
7 checked tic box 10.95 volts everywhere except blk/wht to grnd which is 6.19v not 6v as per manual
8 checked #1 pickup coil its .708k ohm, #2 pickup coil is .704k ohm.
Ive checked for spark 2 ways. Ive grounded the plug to the head-no spark, Ive used my spark gap tool that connects between the plug and the wire-no spark.
Is it just that the battery is low? Its strong enough to spin the motor so shouldn't it be enough to make a spark? Am I overlooking something simple??
Any advice would be great. Im ready to ride before the weather gets to hot.

[IanDMacDonald]

Hell yeah I got some advice for you! Check your battery first! Clean & check all connections EVERYWHERE! Get rid of glass fuse box if still equipped. Clean all switches. Charging voltage should be 12.6v at the minimum. Should be seeing 13.2v almost always.

[CaptonZap]

Here's a quick check of the TCI operation.
Set your V meter on 20V DC, and put the black lead on a good ground, and the stick red lead into either of the outer wires on the 8 pin connector on the TCI. Either orange or grey. You can slide the probe into the socket in the connector and make contact with the spade connector that is trapped in there
Turn on the ignition switch, and you should read battery voltage.
Now hit the start button. The voltage should drop down to 3 to 5 volts while you are cranking the starter. Now try the other one. You should get the same reading.
This is for a standard ignition, but it shouldn't change much with your 3 ohm coils.
If either of the wires do not read that, the chances are that either the pick up coils are open, or there is a defect in the TCI.
Here is the theory:
The ignition switch sends battery voltage to the coils through the red/white wire, and when the engine is not running, the TCI acts as an open switch contact for each coil to ground. So that is why you read system volts.
As soon as the TCI gets pulses from the pick up coils, the internal circuitry starts acting like the points of a Kettering ignition system, which is when the points, (switch) close, the field builds in the coil, and when it opens, the magnetic field in the coil collapses, and makes a spark.
When the TCI is not trying to operate, the voltage at the orange and grey wire is at system voltage. and as soon as the TCI lets current through the coil to build the magnetic field, the voltage goes down, since it is not restricted by open points. (transistors in this case, but the function is the same.) When it shuts the current off, (open the switch/points), the voltage rises. An oscilloscope will show the voltage as a saw tooth pattern, which you don't need to see, since all you are trying to find out is if the TCI is turning the current through the coils on and off. And that will show up as a reduced voltage reading. Your meter is actually reading a pulsed DC voltage, but that is good enough for our purposes.

Good luck, CZ

[Brent]

something simple?

Is it just that the battery is low? Its strong enough to spin the motor so shouldn't it be enough to make a spark? Am I overlooking something simple??
Any advice would be great. Im ready to ride before the weather gets to hot.[/QUOTE]

I am told that with any electrical problem, first check main ground connections.

I solved no spark problem on my XS by cleaning the connections in red/white wire on ignition circuit. A spade conection behind Right side cover near solenoid. Another connection on same wire circuit under tank. My kill switch also crumbled to pieces when I cleaned it, (better at home than on the road).

Good luck wrenching