Magneto advice needed

[bikerbob]

My 1956 A7 will not run at any throttle opening above a fast tickover and even then it is missing, any attempt to go with a higher throttle and the missing gets worse  and it will cut out. I have eliminated any fuel related issues the carb has been stripped and rebuilt no problems with fuel lines or vent in the tank so am left with a magneto problem have tried changing plugs checked pick ups all ok plugs spark OK when turned over with kickstar, points also checked out. Now I would like to know if this is a condenser problem or an armature problem if condenser I may go down the Brightspark replacement method but if it is armature related I may go for the Thorspark electronic ignition route as a complete magneto overhaul is at the moment to expensive. Any advice would be helpful Thanks.

[Roger (Doomtrainbarx)]

Pick up brushes too soft and carbonated slip ring maybe ? - does it start easily ?

[BigJim]

Check to see if the cam ring has shifted. Assume the bike was running normally recently? Mine slipped/shifted and would start and idle but missed like crazy when ridden.

[Triton Thrasher]

Manual or auto advance?

[bikerbob]

Thanks for those replys it has auto advance it is not the pick up brushes but will check to see if cam ring has shifted. It was running perfectly before winter layup but have done the usual winter service oil change check plugs points etc but when I took it for a quick run about month ago to test sfter service it was missing very slightly but thought it was old fuel, so put in fresh fuel went for a longer run a couple of days ago and it was missing when changing gear upwards but was runnnig Ok when getting to about 50mph. But after about 10 miles it started to get really bad could not open throttle above fast tickover without major missing set off back home and had great trouble pulling away from standstill could not open throttle enough for smooth takeoff. Just managed to get the bike home,if I had to pull away on an incline I would not have been able to get enough revs to pull away lucky all my moviong from standstill was either downhill or  on the flat.

[muskrat]

G'day Bob.
I know jack about mags but sounds like condenser to me.
Groily or Andrew might see the post and shed light on it.
Cheers

[edboy]

hello,
it could be running on one spark plug only.

[CheeserBeezer]

Unfortunately, if the usual checks have been done, sounds like it needs stripping and inspecting properly. Sounds like coil insulation breaking down....maybe?

[chaterlea25]

Hi All
If the condenser is faulty the points contacts will blacken, and there will be a lot of whitish sparking when the engine is running
I had similar symptoms to bikerbobs bike when the slipring went faulty
the mag was firing both plugs at the same time due to the surface of the slip ring breaking down
If you take out both plugs and fit them to the leads, place them side by side on the engine
Kick the engine over and look for both plugs sparking at the same time

John

[bikerbob]

Furter update the cam ring has not turned, but that was a good idea chaterlea to put both plugs together on one side of the engine never thought of that before. Most of the time both plugs were sparking in rotation but there were times when either plug would not spark and also I am sure there were times when both plugs seemed to spark at the same time. So am now convinced I have a maneto problem so looking to go down the thorspark electronic ignition route cost is about £150 I remember some 20 odd years ago I bought an exchange armature from Draganfly it cost £45 have looked on their website and they now want £182 so Thorspark looks a good bet.   

[BSA_54A10]

Funny you should post this right now.
The M20 did yesterday with a failed bearing in the maggy
However one of the  things I use a lot is a red in line spark tester ( from a mower parts supplier )
Being red you can see it in the daylight and being in line you can fit it and watch it while you ride ( or run the bike )
If it is a sparking problem the tester will not flash when the engine misses
So if it glows aconstant red whie the engin is faultering then it is not a sparking problem .
I have a colorTune for doing the same thing .

[bikerbob]

Just as an extra test to confirm it is the magneto I bought a set of those red testers from the local Machine Mart shop they come in a set of 4 for just under £14. they confirm that it is a magneto problem.

[BSA_54A10]

That sound cheap.
I gather they are the replacement plug caps used by custom car builders & hot rodders .
Never thought of using them on the bike.
I bought a set to use on mowers ( which I repair ) as I keep on leaving my real tester on customers mowers

[bikerbob]

They do not replace yuor plug caps  they go inbetween your existing caps and the spark plug they flash in time to the spark so mine are not running constantly they are  missing intermitantly on both cylinders on tickover and get worse as you open the throttle.

[Bsareg]

If you clean the slip ring, does the problem clear for few moments ? Have you tried drawing a line with the brushes, if you can see the line clearly, they are too soft. There's still a lot of crap ones about, they leave carbon on the ring bridging the brushes causing strange effects. Cost nothing and worth a try.