R26 starts & then stops

Begonnen von BSA Bob, 14 August 2023, 01:29:03

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BSA Bob

The R26 began stopping when on a run. There was no spark at the plug. After a while the spark would return. This got worse until one day it had to be trailered. Since then I've checked wiring connections, tried an old Bosch coil that tested OK, fitted a new capacitor, points, high tension lead, plug cap & a couple of plugs.
Now it starts with difficulty & runs up to a minute or so before briefly running rough & cutting out.
Perhaps I've got more than 1 problem.
Any ideas appreciated.

BSA Bob


Heiko

Hi Bob,

Try a new coil, doesn't matter either inside or outside coil. The new condensor still works fine?
Ariel motorcycles... upon which the sun never sets.

strichzwojan

Hello Bob,

just in case you have a voltmeter... Check the battery. A weak battery weakens the spark on low revs.
As Heiko said: most likely it is the coil. You can check, if there is any difference when driving without the "Lima"-frontcap mounted, if you got an internal coil. Better cooling ...

Jan

4Taktix

Hi Bob,
is the "old Bosch Coil" similar to the stock R26 coil, or a "big" one, intended for cars originally ?
The latter ones do have a significant higher draw and thus can cause weak batteries to "give up" sooner.
You will notice a weak battery by intermittantly dimming the control-lights while kickin.
(everytime the points close and the coil feds)
Does it make a difference in running time, when you drive with mainlights on or off ?
Plug-cap must not have e.g. 5 k-ohms resistance ! 1K or none is suitable.
Also stock-regular high tension wire works best, please no fancy, hightech, astronautic, silicone stuff.
You should also check, if the breaker lever can swing without any resistance, but also doesn't wobble
or move sideways on it's pivot pin. It can happen, the bushing pinches a little when hot.
But I'd say a minute or so is too less time to warm this up noticeably.
Just a thought.

Cheers,
Sascha
Think outside the box !

cledrera

Hi Bob,
test an ignition coil for a BSA-Single.
Something like an Lucas 6V Ignition Coil, 6 Volt - LU47275.
Maybe ignition coils for Yamaha XT500, DT125/175, 6V, also fit.

Good luck

Clemens
Du bist im Recht; nun sieh zu, wie du da wieder heraus kommst. (v. Chamisso)
Lieber Einzylinder als zwei Fallschirme (v. mir)

rolf

"he latter ones do have a significant higher draw and thus can cause weak batteries to "give up" sooner."


but they produce sparks eveb the Battrey is very low...my 12 V Bosch coil produce sparks down to 4,5 V!

rolf.soler

#6
if the battery is fine, it's probably the coil OR the capacitor. Unfortunately, even brand new capacitors can be bad. Some of us use capacitors from electronic parts dealers instead of motorcycle parts dealers.Caps can temperature sensitive, too, like the coil. They stop working initially when they are warm, before the fail altogether. Try first new caps (one or two...) before changing the coil.
Coil ist more likely, but much more expensive, so try the cheap parts first...

cledrera

Du bist im Recht; nun sieh zu, wie du da wieder heraus kommst. (v. Chamisso)
Lieber Einzylinder als zwei Fallschirme (v. mir)

BSA Bob

Thanks for all these replies.
The coil fitted to the bike is a genuine BMW coil for the R26, new old stock. The "old" coil I tried is a 6v automotive coil fitted to the bike when it last ran, probably from a VW. It was fitted under the tank roughly similar to an R27.
The battery's in good condition.
But I think I've fixed it. A bit embarrassing I know. Both coils stopped sparking, a dim light went on in my head & I checked the wiring yet again. With the meter I finally found a bad connection between the 15 terminals. I'd checked this & the other connections with the meter before, it was tight & I couldn't pull it apart. It looked good, nothing wrong with it except that it didn't work. I think an intermittent & then failed connection would create all the symptoms I described.
So now it starts easily & seems to run OK. The weather here's dreadful at the moment so a road test will have to wait.
Thanks again for the ideas & information.

cledrera

Du bist im Recht; nun sieh zu, wie du da wieder heraus kommst. (v. Chamisso)
Lieber Einzylinder als zwei Fallschirme (v. mir)

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