Electronic ignition wandering spark

[limeyrob]

Is it manual A/R or auto? I much prefer manual but it has the disadvantage that it moves the spark away from the best flux point.  With an auto the mag is always at its best point.
I've recently been round this loop on my RR (K2F). Hard to start and weak spark at idle.  I have a box of old mag bits so I stripped it down, swapped a few bits, cleaned everything, put new brushes in and now its fine. There was no obvious fault but it made a big difference.

[rhyatt]

Ah ok.
Dare I ask if you were using a resistive spark plug cap ?
As you should not have anything in the way of the spark leaving the slip ring.

No resistance at all , just pure copper ht lead , plain cap , non resistor plug

[PeteB31]

limeyrob.

The bike has a manual advance / retard lever on the bars. I'm loath to send the magneto away for an overhaul as I can't categorically prove it's performing below bar. The electronic ignition seemed a low cost option and certainly worth a shot. Total spend so far is under £50.

rhyatt.

Champion spark plug. 10k OHM.
Copper core HT lead.

Pete

[rhyatt]

I assume the 10kohm is the resistive plug cap.
Do away with it.
Mags have never advocated a resistive plug cap.
Non resistive screw on plug caps available green spark plug company.

While that's coming in the post, just wedge the end of the naked copper lead in the fins and give it a kick , 1/4" gap should give a good blue crack of a spark

[limeyrob]

Yes, sending the mag away may not be needed, but a clean up on the bench may work.  Your electronic ign set up looks nice, its just a pity that its doing something odd.  Pardon my ignorance, but how are you keeping the manual A/R?

[PeteB31]

rhyatt.

We will try different HT lead and cap fixing options during the bench testing. The original lead was a heavy gauge copper lead with a spade end screwed directly to the top of the spark plug.

limeyrob.

The advance / retard works in exactly the same way as the original points. The whole assembly is retained by the same sprung ring as the original cam washer. There is a notch in the lower plate that is activated by the advance / retard cable nipple. So the whole assembly moves through 20 degrees or so as operated by the handlebar lever.

Pete

[rhyatt]

The reference to non usage of a resistive plug cap applies only to ht systems when used with a magneto only.
Any other coil based ignition can utilise a 10k plug cap

[limeyrob]

Thanks for explaining the A/R, that's neat, I couldn't work that out.  Will you leave the mag armature in or run a dummy shaft? The mag could be generating a lot of electricity with no where to go.

[V500]

If the points plate is missing there's no HT "load" generated.

[Derek996]

Thanks for explaining the A/R, that's neat, I couldn't work that out.  Will you leave the mag armature in or run a dummy shaft? The mag could be generating a lot of electricity with no where to go.

The Thorspark electronic conversion retains the manual advance\retard in exactly the same way.

[Janacek]

Is it manual A/R or auto? I much prefer manual but it has the disadvantage that it moves the spark away from the best flux point.  With an auto the mag is always at its best point.
I've recently been round this loop on my RR (K2F). Hard to start and weak spark at idle.  I have a box of old mag bits so I stripped it down, swapped a few bits, cleaned everything, put new brushes in and now its fine. There was no obvious fault but it made a big difference.

That's interesting.My B31 has a rather 'Lumpy' tickover on full advance,but pull the lever back an inch or so,and it chugs away nice and evenly like a cement mixer.
Checked the ignition timing,but never thought about the magneto flux.

[iansoady]

That's quite normal in my experience - full retard should give a better idle as on full advance the spark is occurring too far before TDC.

[V500]

Retard should give a slower idle, but dunno about "better".