Magneto starting to fail?

[Duncan R]

Hi All,

Grateful for any feedback on a problem I have at the moment.

I was out for a run yesterday and after about 30 miles or so I was travelling down an A road with the bike happily sitting at around 60 MPH mark,then all of a sudden the motor just cut out ,no misfire just a complete shutdown. I coasted to a halt and started to have a look around the engine to see if I could find the problem. In the bright sunlight it was difficult to see if the plugs were sparking when I turned the motor over. I had a pair of spare plugs which I fitted and the motor started fine and I rode the 30 miles back home with no issues.

Previous day I was out on a run and the bike was difficult to start after a short break by the roadside. I did have some misfires on small throttle openings and when loading the engine in the higher gears. After the starting issue the bike ran perfect with no misfires for the rest of the ride.

The magneto was rebuilt in approx 1999, the bike was then laid up in 2001 to 2009 as I was working overseas. Since the bike has been back on the road it has run fine it starts and idles very well.

I suspect the mag is breaking down now - Is there anything else I should be looking at?

Thanks for your time

[Triton Thrasher]

Check the free things first.

Is the vent in the petrol tank cap blocked?

Are all the petrol gauzes clean? Is the carburettor free of water content? Is the float or needle sticking?

Are the points clean and gapped? Is the points spring clearing the cam?  Is the HT slip ring clean? Earth brush & track?

Does it behave better if you close the plug gaps to about 5 thou? That might indicate magneto trouble.

Someone is probably going to suggest trying the Easycap replacement condenser.

[madsens]

Hi
I got in trouble after a total engine rebuild - bike had been running ok before i tore it down, then had a standstill for about a year when I got the engine rebuild, and put together again.
During run-in it started ok, but when ou ton test run it started to misfire and spit back when it got a bit of stick. Eventually ended on a trip with total misfire and only running on one cylinder. Coasted home to a nearby bikefriend and me and friend swopped to another carb, but to no use.
 I had to go to work at sea after that, and during this my friends worked on the bike ,checked and adjusted timing, and managed to start it with the points end cap of, and there were sparks all over the place!
So he did the famous Condensectomy and fitted a Brightspark Easycap, and thats hopefully the end of story... Just did a couple of test drives since, but bike is now running great, and easy started again, thanks to the good work of great friends!
regards
Joergen

[Duncan R]

Thanks,

I am 99.9% sure ther are no issues with the fuel side. I will check the pick ups/ slip ring as I am getting some oil in that region from a top end leak

[Duncan R]

Hi Joergen,

I am going to give the slip ring a good clean as I could be getting oil in there from a leak (see post in engine section) Funny thing was after both incidents the bike restarted and ran perfectly

[beezermacc]

You say the magneto was rebuilt in 1999. Do you know what was done? It probably needs inspecting to check that everything was done properly.

[Duncan R]

The Magneto underwent a full refurb by Fred Cooper in Kent, a very respected engineer who sadly passed away a few years ago. It has been faultless up to now. I did read somehwre that mag performance can tail off over time, it has been 15 years since the rebuild and for 8 years the bike sat in storage.

[BSA_54A10]

had a similar problem way back when I had hair teeth & no fear.
Bike would start to play up after about 1/2 to 3/4 hour.
So I would stop. drain the float, check the points, check the timing. check the tappets etc then it would fire up & go like a rocket (for another 1/2 to 3/4 hour ) but by then I would be home.
My continued ability to fix my bike on the side of the road got me a reputation of being a mechanic extroadinre .
Any way on the way to the beach one day it died, stopped dead & refused to go not a hint of a spark.
Now the brushes were getting very short and havine just past an sparkie I though I might just replace them.
And not thinking properly I just walked in & asked if he had a set for an A10 which he did , ( remember those days ?)
Any way when I went to replace them they were totally different to what was in there so I got a bit shitty and went back with both the "wrong" ones & what I was running.
the sparkie just looked down at me & said, "funny your are running Bosh brushes in a Lucas maggy, normally the springs go soft & they loose contact with the slip ring after an hour or so".
Being by myself the only damage was to my ego & pocket as he charged me 5 bob for the brushes ( a beer was only 6 p in those days ).
Naturally I told my clique that I had "done up" the maggy to explain the nonexistance of the regular stops.