Pickup coils

[DEmily]

Hey all,

Been driving the BIGDOG as much as possible since I got her going. Just started having a problem with number 1 and 4 firing. Did the pickup coil test and found a bad wire. I fixed the wire as the tech tips suggest and replaced it gapping a .006. Still no fire to 1 & 4. Checked for continuity from the CDI box all the way to the pickup coil and all tested good. Is it possible that the pickup coil is bad? Can I test the thing?

[Ken Talbot]

It is possible that the pick-up coil itself is bad. It is also quite possible that you've got more than one break in the pick-up coil wires. The latest break I found on SWMBO's 'H was at the crimp just before the wire bundle leaves the housing. That one took me a long time to isolate.
YMMV....

[rover]

I just bought another 79F last Dec (xmas gift to myself), and have been chasing pick-up coil wire breaks, after finding the fifth one, I bit the bullet and ordered a new set from Bike Bandit for $110 delivered. Problem solved, the bike runs great even without messing with the carbs. I wish I would have done this right away.

[randy]

Dan,

Pickups should read about 600 ohms. Measure from the connector at the ignition box and test the whole harness through to the pickup coil. Also check the permanent magnet in each pickup coil. A small screwdriver should be attracted to it fairly strongly. Do this WITHOUT the bike running.

The magnet is an important part of the pickup. If it's lost it's force, the pickup will test good but it won't generate a firing signal. As the reluctor passes the magnet, the reluctor transfers some of the magnetic force to the coil, inducing a signal. That signal is then amplified inside the ignition box to switch the coils.

Also, take note that ignition circuits 1&4 and 2&3 are discreet circuits from the pickups, through the box and into the coils , they don't 'join' inside the box, so it is possible and I've seen it, that one side of the box is faulty. This symptom is usually a cold solder joint inside the box.

HTH

Randy

[DEmily]

Oh Randy, Don't say that ! I sure am not comforatable with breaking open the box! I'll do it if need be, but I cringe at the thought. I have tested from the plug at the box back and got 720 ohms on both pickups. The odd thing to me is that it ran soo good for several hundred miles, then went. Of course I found a break in the pickup line by pulling the wire and watching it strectch about 6 inches. It was obvious. But you would think once that was repaired, it would be back to normal. I plan to chase down all the wiring , including to the new accell coils. Maybe I just have a coil that is a bit too close to the tank and its grounding out. I'll fine out soon hopefully.

[randy]

Yeah, 720 is good 600-800 is the range. BUT do you have 720 WHILE YOU TUG? Could be intermittent.

Don't worry too much. Those boxes aren't magic, you know. You can send me the box and I'll help you out. Let me know what you find,

Randy

[DEmily]

Randy,

Thanks for the offer., I'll keep it in mind. When I got 720 on the pickup coils, that was after I repaired the break.

[DEmily]

Hey everyone,

Well, I checked the pickup coil and it is still magetic. I deceided to switch pickup coils as I knew the other one was firing. Still no fire. I noticed when I cranked the started no spark, but as soon as I turn the key off the plug would jump a nice blue spark. I turned the key off and on, nothing. I crank it a few times and then turn the key off and a spark? Any ideas.

[randy]

Dan,

What you're seeing is the coil responding to the loss of power. In operation, the coil actually produces the spark when it is switched OFF. Kinda backwards you might think, but it is the magnetic field inside the coils collapsing that induces the high energy 'kick' to produce the spark.

As in a points system also, the spark occurs when the points open, cutting off the juice to the coil. Ours works the same way, only electronic switching.

I'm curious, you said you switched the pickups. How? did you re-wire the plug at the box? If you swapped them and still no joy, then I'm sorry to say, it sounds like your TCI box is sick.

HTH

Randy

[DEmily]

Randy,

Well, now both sides have stopped firing. I put the pickup that was working back in it's original position and regapped, Nothing.

This is becoming a very expensive bike that I have hardly rode. I have just about replaced everything on this thing that can be replaced except in the ignition. Now it wants to fail! Damn!!

When checking the voltage to the coils, should both post on each coil be showing 12 volts? Thats what I am getting.

[DEmily]

Randy,

Let me be a bit clearer. When I test the two post on one coil, with the key on, I get 12 volts at both. When I disconnect the box I get 12 volts at only one post on that same coil. This hold true for both coils. Is this what I should be seeing?

[TheDjost]

One side of the coil is wired directly to the battery (through the ignition switch). The other side is connected to the TCI box. In operation, the TCI sinks the coils to ground, creating a 12V current flow through the primary. When the pickup coil picks up a pulse from the magnet, the TCI stops grounding the coils, in effect breaking the circuit, wich in turn, provokes the high voltage kickback on the secondary.

It's the same effect that forces relay manufacurers to put a small diode in their relays... to sink to ground the high voltage kickback the coil produces when they are shut off. A lot of relays were fried before this was found out.

If you have 12V continously at both termicnals of the coils, I would bet that there is a problem with the TCI, or the pick-up coils. If it's the TCI, they can be repaired quite easily by somone with electronics repair experience. I think Randy and a few others even indicated thet they could do it. Most of the time it's just a bad solder, and sometime the final transistors go bad. They are not very expensive to replace.

-Justin

[DEmily]

If the pickup coils sends a pukse that disrupts the ground, can that pulse be measured with a meter?

[Ken Talbot]

Sure sounds to me like you've still got one or more breaks in the pick-up coil wires. You have a pick-up that was working, but with some swapping around, not it doesn't work even when put back where it used to be. Surely the pickup itself could not have suddenly gone bad, nor could the coil of the TCI box if they weren't bad before. Open up all the crimps that hold the wires in place. Look for more breaks. I'm positive there's more to find.

[DEmily]

Ken,

When I test the wires from the tci box to the pickup coils, they both read 720 to 750 ohms. If I had a break would I get a reading at all?