Posted by JAW - the XR has always been very hard to start. At first people would say "heh, yeah, those single pot 600's are bastards to start." When JAW was starting to walk around in circles because his right leg was twice as big as his left leg, he began suspecting carby troubles. "It only starts when it has the exactly the right amount of fuel in the pot it seems. Too rich, it wont start. To lean, it won't start."

Finally Wise Wolfie said "JAW check your spark." "Yeah, it sparks Wolfie, it wouldn't run at all if it didn't spark!" "Humour me."

Set yourself up first, you want to be able to drag wire off the spool easily.

Weak spark?

Behold and lo, the was the wimpiest pale spark you've ever seen; it would have battled to fight it's way out of a wet paper bag. That kinda makes sense - a fat spark would ignite fuel in up to the worst conditions, but a wimpy spark would need "perfect" conditions to get the show on the road. Well that's what JAW thought anyhow.

So what does a weak spark mean? If you look at a bike sparking system there is the spark plug, the ignition coil, high tension lead, wiring, the pulse sensor, the CDI and the stator exciter winding to generate the power. A few things there are easy to test and I'm sure you know how ;)

JAW finally isolates the problem as being either the CDI or the exciter coil. Do you think you can get a motorbike shop to test a CDI? "Hey guys, have you got an XR600RJ that you can verify the operation of this CDI on?" "Oh, no no no, you must go and pay $'00 to the Master Motorbike Electricals Guru, it's all magic, only he knows how it works. Blah blah blah.

Gotta be the exciter winding...

JAW makes a bold decision: "CDIs are electronics. They either work, or they don't work. Okay, so maybe the big cap in it will deteriorate over time but I reckon that tiny, thin winding of enamel wire that is subject to heat, oil and works from a permanent magnet is *far* more likely to be the problem. I'm going to rewind my stator exciter coil.

Find yourself a big spool of hair-thin enamel winding wire. Very conveniently this big spool was in the olde man's shed. .132mm, with a 1978 date stamp on it ;) It's fatter slightly than the existing windings though. Oh well.

The old exciter winding, yeah, the big winding at the top.The other 4 windings are separately regulated for the 12V bike supply. They are thick wire small number of turn windings for lower voltage and bigger current (up to 50W say). Ideally I'd like to see a whole ring of them, as when parallelled up they produce more current. Did anyone ever mention that the headlights on XRs are pathetic?

The empty pole, ready to receive some wire...

Rewinding, a process.

Rip off the old windings. Be careful not to break anything ;) If you can work out which way the winding went, good. If you can't, don't worry so much. It's AC power, it can go in either direction. Note this winding for the exciter coil is a single winding, whereas other bikes such as an RM250 have six individual coils to make the one exciter winding. Yikes!

The scoop is that a factory XR600 85-90 should have an exciter to ground resistance of 230-320 ohms. My old one was about 370. Can't quite explain that, perhaps over time the wire slightly corrodes or thins in points and increases the resistance? Anyhow, open circuited the ols winding was good for 40VAC which you'd think must be enough, but with the increased resistance the current flow just isn't there and the in-circuit voltage is right down.

Because my new wire was marginally fatter, the resistance would be lower over the length of the wire, so I figured I'd better do more windings than was previously on there. Which was a lot.

Halfway - careful does it!

First attempt done - measured only 162ohms, the factory spec a minimum 230ohms. Spark improvement, but not enough for my liking...
Make sure the wire can freely pull off the spool and just wrap, wrap, wrap. It's suprisingly strong for hair-thin wire but don't take any chances. Do a few stress tests on it before you begin, see how easy/hard it is to snap it . You want one winding, you don't really want any joins. 

After about an hour, yeah, just an hour, it was wound to where I thought it should do. Slightly bigger than the old coil. Big tip: carefully peel off a bit of enamel and do a resistance check before cutting the wire.

I cut it, and the resistance was 162ohms. A bit low, but nonetheless I carefully soldered on some flyleads and expoxy'd the thing in place to protect those precious little windings. I used some devcon I had lying around, it isn't conductive, it is tough as, it did the job.
Protect your windings.

Second attempt - I made a superhuge coil that measured in at 250ohms. Much better, you can actually hear the spark crack!


Okay, the winding was a success. The bike started, but it is still hard to start, maybe there are other problems. I wasn't satisfied - so I ripped off the winding and started again. I noticed while pulling my first effort off that the windings are no where near as tight as a machine spun winding. On my second effort, I wound and wound and wound until I measured 250ohms, and the coil was starting to become physically a bit big. I cut it there and re-epoxied it.

More windings, more voltage. The spark is now fatter and bluer, just like a spark should be. Of course more windings means lower current, but CDIs don't need much in the way of current, it's the high voltage it wants. Now she starts almost first kick everytime, even when cold! Whats more, after the first "burn in" run around the Alkimos dunes where *all* bikes get hot, the new winding still works! ;)

So the key learning is that yes, you can rewind your own exciter coil, or any of the coils for that matter, and it is pretty easy - there is no magic involved at all. Just wind, don't break the line and stop when you reach the required resistance ;)

The second attempt all poxied up. Yeah, a bit bigger than stock.

The stator bolts into the rotor cover.
How the stator would look sitting in the rotor.

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