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Lucas Mag

macvette

Well Known and Active Forum Website User
Non-VOC Member
Not strictly Vincent but I'm sure someone here will know the answer. I've recently got a 1937 BSA Empire Star and am tinkering with it over the winter. After having problems starting ( it wouldn't because of badly adjusted tappets), it now starts easily and idles well once warm. The thing is it, occasionally misfires when idling. When it does this, a spark jumps from the nut on the centre of the drive end cover of the mag to earth with a healthy crack!

I haven't ridden the bike yet so I don't know how it performs under load. Any suggestions?

Mac
 
Last edited:

greg brillus

Well Known and Active Forum Website User
VOC Member
Hi there, i'm assuming it's a magdyno.....first check that the spark plug is in good condition with no more than an 0.018" thou plug gap and check that the HT lead is in good order, that is, not oil soaked or damaged. Next i think from memory a magdyno doesn't have a safety gap built into it, which is like a safety fuse for the high tension voltage to escape to if the HT lead came off the plug. So if you can get to it, pop the pick up out of the side of the mag and have a good look at the slipring, perhaps rotate the engine slowly whilst cleaning the slipring with a bit of petrol on a rag. There is a good chance that you may see either a piece missing or a crack in it, or it could be just badly worn. Any of these faults will cause the missfire you describe, as the spark is always trying to find the easiest path to an earth. Hope any of this helps, cheers......Greg.
 

clevtrev

Well Known and Active Forum Website User
VOC Member
Not strictly Vincent but I'm sure someone here will know the answer. I've recently got a 1937 BSA Empire Star and am tinkering with it over the winter. After having problems starting ( it wouldn't because of badly adjusted tappets), it now starts easily and idles well once warm. The thing is it, occasionally misfires when idling. When it does this, a spark jumps from the nut on the centre of the drive end cover of the mag to earth with a healthy crack!

I haven't ridden the bike yet so I don't know how it performs under load. Any suggestions?

Mac
There`s a hole in the insulation , somewhere.
 
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