spark plug lead attachment to magneto

[AndrewM]

I have been getting my 1946 AJS Model 16 running properly, after finally giving up on the old leaky carb and buying a brand new one, correct for the bike (i.e. Amal 76D/1J). After installing the new carb and replacing the broken tufnol spacer, the bike started second kick and ran beautifully, except at idle, where it idled a bit high and rough.

This improved after playing around with the idle mixture, which not surprisingly ended up at exactly and a half turns out on the idle mixture screw, the recommended value.

Idle was still a bit high and a bit rough, so thought to check the spark plug cap, which turned out to have a resistor in it. I have ditched this and am waiting for a new lead and unsuppressed plug cap in the mail. In the meantime I started to look at the inner end connection of the spark plug lead to the magneto, which I found was loose and pulled out surprisingly easily. I unscrewed the collar and found it to be parallel with no form of clamping mechanism (see photo).



Is there supposed to be some form of clamping mechanism to hold the spark plug lead into the magneto, such as a compressible O ring? How is this supposed to work?

[g5wqian]

hi Andrew;
usually there is a flat brass split washer below the collar which is on end of the HT lead , you would have about 1/4" of wire exposed from end of HT lead and this passes through the brass split washer and the wires are bent over and spread around the face of the washer , then the face of end of the collar holds it in when its all screwed down .

you can get the split washers from places like green spark plug company or likes of ebay , maybe even club spares have them .

you may get a tighter fit if you can find some 8mm cable as opposed to the 7mm mostly sold now , if you can find american car solid copper HT lead they usually use 8mm , otherwise you could put a short bit of black heatshrink tubing at end of lead where it enters collar etc .

there are also some HT connections where you screw the HT lead into it so i am not fully sure which type you have there , but if its like my K2F magneto style it will use the brass split washer .

https://www.gsparkplug.com/ignition/dis ... l-fittings

hope you get it sorted the way you need it .
ian

[Andy G]

Take a good look in the magneto ole....the split washer may have been left in there!

[AndrewM]

Yep, checked the magneto pickup and the split washer is long gone. I've bought a complete new Magneto pickup which includes the washer, an expensive way of replacing a component worth about ten cents. But the old pickup is probably 76 years old so most likely due for a refresh.

g5wqian, I might try the idea of the short length of heat shrink to get a tighter fit, the old cable was very loose so surprised the bike was running at all.