A problem the bike had when it was laid up 6 years ago has resurfaced- poor starting.
It usually starts reasonably well from cold but is almost impossible when hot. There doesn't seem to be any spark at these times.
I've checked the pickup & HT lead, the earthing brush & the CB unit (a sloppy fit on the mag spindle, new unit coming).
Once the bike's started it runs fine.
There's no sparking at the points.
Can anyone think of something I've missed, or is it time to get the mag rebuilt?
Sounds like the classic “weak mag when hot”.... if you don't know the history on your magdyno, it’s reasonable to assume that it’s become old and tired. Time to refurbish...
email (option): teladelujo@msn.com
email (option): ronpier@talk21.com
Hi Rob
I had a similar problem and thought that the condensor was on its way out.
However, I checked continuity (using a multi meter) between the end of the carbon brush on the mag pick-up and the end of the HT lead and there was none. A new brush for the mag pick up sorted it out.
Worth checking......perhaps you have already.
Regards
Pat
email (option): sacombsashtrees@hotmail.com
My mag stopped working, I'd had it rewound so it couldn't be that and everything else was good too. I took it off, took the brushes out that looked like new. With a clean cloth I put my finger in the hole to the mag ring and turned the spindle. The cloth was black with dirt. I used some meths and throughly cleaned all the connections and don't forget the earth brush. The mags been fine since.
email (option): horror@blueyonder.co.uk
Re horror
The dust inside is due to cheap nasty carbon brushes that come in a green lucas box that are from India this dust then gets on the bearing that wears out pretty quick the best way out is find a good second hand one or a new red packet genuine lucas I got a new Stanley knife blade scrapped both 10 times and was shocked at the difference of carbon dust this was when I had my bike shop many years ago.
email (option): malmotorcycles@gmail.com
My second M21 had a useless spark when hot. I used to close the gap ride it to a hill and then open the gap up again and bump it. This was a bike about twenty years old so God knows what state an original mag is in with another forty five years on the clock
email (option): j@clogmaker.co.uk
Thanks for the response folks. I should've mentioned that I'd cleaned the slip ring too. The new contact breaker unit has been fitted & there's no spark at all at the moment. Whatever, it's beaten me so it'll come off for a professional to look at.
Incidentally, the new CB unit was very tight to fit. I've never had to fit a new one before. Can someone let me know if this is usual?
“Incidentally, the new CB unit was very tight to fit. I've never had to fit a new one before. Can someone let me know if this is usual?”
First question I would ask; is it a genuine Lucas item or an aftermarket reproduction? Reproduction parts are notoriously prone to “not quite fitting” to won’t fit at all.
Also, over time the contact breaker mounting “step” on the magneto armature can become a bit distorted from a loose CB assembly or from decades of being wanked over the history of ownership. If the breaker assembly is not at fault, I would look for any wear or damage on the points end of the magneto armature,
email (option): teladelujo@msn.com
Hello Bob.
Another thing you might want to check,
Is if the new CB block has an isolator between the 2 parts of the assembly,
And if I remember correctly, also inside the screw hole.
I am sure that you checkecked it, but sometimes the points do not close all the way,
If the points "pusher" or whatever it's called, (Goes from the mag cam up through the CB block to push the top ponit)
Was replaced and it is longer that the previous one.
Many of the Indian replacements are made of brass, so it is a good indication, but not always.
I fitted an Indian CB for a friend, and ended up placing the worn original one back.
The replacement was really BAD...
Noam.
email (option): noam10@gmail.com
John & Noam
Thanks for the ideas. Yes, it is a pattern part. I had to file a bit off the rotor arm to get it to fit inside. And I had to tap it lightly to get it on the mag spindle. I checked that there are insulating parts. I suspect that the CB's OK & that it's the main part of the mag that's at fault. We shall see.
Hi Bob.
You mentioned cleaning the slip ring.
There are 2 brushes on the mag.
I in earth/ground and the other one is under the pickup.
Both are spring loaded. did you inspect them both?
Noam.
email (option): noam10@gmail.com
Hi Noam
Sorry to take so long to reply- no internet access over Christmas.
Yes, I've checked all the brushes. The maggy's at the specialists now, so I'll wait & see.