Spark between pickup and housing

[roadrocket]

Hello All!

On an altogether wonderful one week trip to Western Norway (somewhat close to Erlings home), I had some troubles when setting off from stationary. This turned out to be linked to the fact that sparks were flying from one of the pickups to the manual A/R cable fastening on the magneto housing. Big fat 2 cm sparks! I turned the pickup 180 degrees, and problem was solved. But I don't want to carry on like this, and want to fix the roots of the problem. I have tried a search, but couldn't find a thread dealing with this. I have forgotten some prior knowledge of this, so please refresh my memory, even if this is common K2F lore.

Best regards, Otto ffrom Denmark

[RichardL]

Otto,

I am thinking you may be using modern spark plug wire intended to reduce radio noise. This wire uses a carbon impregnated core that is higher resistance than stranded copper. The spark would be taking the path of least resistance and, apparently, there is less resistance in 2cm of air versus about 30 cm of spark plug wire plus the gap of your plugs.

Just had another thought, I could envision that a coating of antisieze on the plug threads could increase resistance to chassis ground.

Could either of these explanations explain the problem?

Richard L.

[coater87]

 Hi Otto,

 I would check for a crack in that pick-up housing.

 Lee

[A10Boy]

How old the pick ups? as with plug caps, the placky doesn't last for ever.

[RichardL]

I guess I misread the first time, not picking up that the spark was jumping from the pickup. At the risk of being wrong again, could the wire have separated inside the pickup, then seated better, when the pickup was turned?

[Brian]

You should not have sparks anywhere outside the maggy, if its jumping from the pickup then thats probably at fault (hope your carby doesnt leak!). The same applies to plug leads and caps, you should be able to hold them when the bike is running and not feel anything. Sounds like its time for a couple of new pickups and leads and caps. If you buy new pickups get them from a reputable maggy specialist that can guarantee the quality as some of the cheap plastic replacements available are rubbish, same old problem with aftermarket stuff.

[a10 gf]

I hope you had an enjoyable trip. Pictures ?

Brian came up with excellent suggestions, tell us how it went. btw, does your mag have the safety gap screws intact?

e

[Josh Cox]

G'day,

Electricity is a predictable quantity, it will take the path of least resistance.

A spark plug gap is around 20-25 thou.

Your spark is jumping approx 2cm.

For a spark to jump through air, the voltage needs to be about 3,ooo volt per millimetre. In this case 60,000 volts.

A couple of issues ?:
1) the Voltage seems a little high,

2) why is sparking from "the pick ups to the case", the path of least resistance ?, as opposed to up the lead and through the plug gap ?.

I would definately be changing the leads, pick ups and plugs just to be sure, but I'd reckon your problem is probably in your magneto, condensors are often the weak link, was the engine still running well ?.

Good luck.

Manosound, most anti seize products have quite a lot of metals in them, particularly nickel, nickel is quite a good conductor.

[Triton Thrasher]

Lets's keep it simple at first- almost certainly a cracked pickup or very damp pickup.  Just for fun, try cleaning up and spraying the pickup with WD40 to see if that temporarily helps.

[roadrocket]

Thanks so far chaps!

I can tell the following about the mag; it was entirely overhauled in 2001, 7000 miles ago, by a very skilled specialist, new windings, new condenser, new bearings etc. The safety screw is indeed present. Everything has been absolutely troublefree, except for some instances where the HT lead has broken off in the pickup. I also checked this when the bike played up on my trip. The restorer made a point of telling me about bad pickups and leads, so I assume he chose wisely, but they are from the time of the overhaul. I got some caps and plugs from a car accesory shop underway, and it didn't help much apparantly. I'll try the metods suggested. I can add that the earth brush was quite oily, but I wiped this clean to no great avail.

[Triton Thrasher]

Your mag probably is good- if it can throw a big fat 2cm spark from the pickup!

Could the inside and outside of the pickup or acorn nut be a bit smeared with chain grease and/or carbon?  That could possibly provide a path for the spark, even without a crack

[MikeN]

Ive had this happen on one of my pick-ups.My bike started running on one cylinder.
The arc was jumping from the p/up to the cylinder barrels .I stuffed a bit of cardboard between the p/up and cyl to get home. When I removed it and examined it there was a fine crack  along the body where the HT cable retaining nut screws in.The p/up was quite new.Im guessing i may have overtightened the plastic(bakelite?) HT nut and expanded and split the pickup body,they are quite brittle.
MN

[roadrocket]

OK, just to follow up on this one; after cleaning and drying out with some compressed air, everything was put back, with a smear of silicone grease on the HT cable thread. All is now well, and every spark is now exactly where it should be. I have ordered new pickups with gaskets this time, perhaps they resist scandinavian climate better.