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Bsa b40 electrical problems #797303 02/02/20 2:59 pm
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Bigmac Offline OP
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Had the b40 for about a year now never had it running so deicide to pull my finger out my backside. Fitted a ne kick start tab cleaned the points had a good spark. Had a few carb issues. Fitted a new carb from Surrey cycles then no spark no lights horn all electrics dead. Put the battery on charge overnight had a quick look for any disconnected wires all looks good. 1961 6volt
Any help would be much appreciated
My first brit so learning on the job

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Re: Bsa b40 electrical problems [Re: Bigmac] #797393 02/03/20 6:59 am
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gunner Offline
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Some thoughts which may help:-
- use fresh fuel and modern fuel goes stale quickly
- use a new plug HT lead & condenser and check the HT load for cracks
- make sure the bike is timed properly, get the workshop manual for instructions
- there are some free owners/workshop manuals on various sites including BSA Unit Singles

Its also well worth buying the Rupert Ratio unit singles manual volume 1 which provides excellent advise.See This Link

Let us know how you get on!

Last edited by gunner; 02/03/20 7:04 am.

1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: Bsa b40 electrical problems [Re: gunner] #797398 02/03/20 9:43 am
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Bigmac Offline OP
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Have ordered a Rupert ratio unit singles this morn. My main head scratch is had lights horn and spark then like a flick of a switch nothing.
After charging the battery and refitting its not even moving the amp meter

Re: Bsa b40 electrical problems [Re: Bigmac] #797403 02/03/20 11:28 am
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gunner Offline
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Sounds like something is wrong with the wiring, I would go through the harness looking for loose connections or broken wires. Maybe a fuse has blown (if fitted) or the ignition switch is duff.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: Bsa b40 electrical problems [Re: Bigmac] #797406 02/03/20 12:39 pm
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Allan Gill Offline
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Im guessing that for 1961 it was a distributer model (not side points)? I am not familiar with these distributers in the slightest so bare with me, if you have any photos they might also help.

I agree with Gunner, its most likely a broken/loose connection or one made in the wrong place.

check with a multimeter that you have a good connection between the points in the 'dizzy' and the + side of the coil, check also that the condenser is grounded sufficiently on the engine and the screw firmly fastened, also that the other wire is connected with the points (or if the condenser is not mounted at the points, but near the coil, make sure the body has a good ground again and the lead is attached to the + side of the coil.

check again with multimeter (set to ohms on all of these, or buzzer setting to save you looking at the meter if it has one) that the points do not have conductivity with the motor, so put one lead on say cylinder head fin (easier if you have leads with crocodile clips) and the other onto the sping steel on the points. when the points open the buzzer should stop or resistance should show "I" (infinaty) or far left on a dial/analoge meter. if you turn the engine over the points should then touch eventually and this should give the opposite effect showing continuity.
The WSM shows this using a battery and a lightbulb but in effect is performing the same function.

If this happens, connect a lead from the battery directly to the negative side of the coil. this bypasses the complete loom.

fit the plug into the plug cap and rest the plug on the head. turn the engine over and you should see a spark. timing at the moment is not crucial. Although it will be to start the bike.

you can then remove this wire and go through the loom and see if the spark happens again. If it doesn't then you need to find that wire in the loom, a long length of wire and going between different points and testing will help, alternately check the continuity of the wires as you work through them.

I mention checking the points first as if you don't have this bit sorted under a simple circuit then you could spend more time at the loom and still be sratching your head.

Good luck.

Allan


beerchug
Re: Bsa b40 electrical problems [Re: Bigmac] #797407 02/03/20 12:48 pm
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Bigmac Offline OP
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I have borrowed a mac test light shows live and earth.
When I test the earth under the seat the tester shows positive but when I test any other earth's it shows negative the tester has a green and red light. Do you think this shows a broken wire that's earthing some where. Also I'm sure when I first put the battery on the amp meter showed battery power with no ignition on.

Re: Bsa b40 electrical problems [Re: Bigmac] #797408 02/03/20 12:50 pm
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Allan Gill Offline
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Can you take a photo of under the seat?


beerchug
Re: Bsa b40 electrical problems [Re: Bigmac] #797409 02/03/20 12:59 pm
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Bigmac Offline OP
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Buy that man a drink it's the ignition switch
Found the old one off the b40 threads were knackered so replaced it
And bingo all was well again
Many many thanks chap πŸ™πŸ™πŸ™πŸ€—πŸ€—πŸ€—πŸ€—

Re: Bsa b40 electrical problems [Re: Bigmac] #797422 02/03/20 3:14 pm
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Allan Gill Offline
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Nice work!


beerchug
Re: Bsa b40 electrical problems [Re: Bigmac] #797427 02/03/20 4:03 pm
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Bigmac Offline OP
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Just collected a new ignition switch all was well for about 30 seconds then nothing again.
Off to work now will check all connections to the ignition 2mora.
Hopefully narrowing it down

Re: Bsa b40 electrical problems [Re: Bigmac] #797428 02/03/20 4:15 pm
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kommando Online Content
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I think the 6V system was fuseless, so best if you add a fuse or you are just going to carry on blowing ignition switches. Fuses are cheaper.

Re: Bsa b40 electrical problems [Re: Bigmac] #797432 02/03/20 4:33 pm
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Bigmac Offline OP
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Good point if I am blowing ignition switches do you have any idea why

Re: Bsa b40 electrical problems [Re: Bigmac] #797433 02/03/20 4:36 pm
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Bigmac Offline OP
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And what size fuse would you recomend

Re: Bsa b40 electrical problems [Re: Bigmac] #797451 02/03/20 5:59 pm
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BSA_WM20 Offline
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Newby problem.
This bike is wire + earth
If you hook it up - earth you will blow whatever is the weakest part every time.


Bike Beesa
Trevor
Re: Bsa b40 electrical problems [Re: Bigmac] #797456 02/03/20 6:58 pm
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kommando Online Content
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7A to 10A fuse.

Re: Bsa b40 electrical problems [Re: Bigmac] #797691 02/06/20 3:24 pm
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stanoneandonly Offline
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Try RJs Hotel St for advice.

Re: Bsa b40 electrical problems [Re: stanoneandonly] #798233 02/13/20 11:11 am
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Bigmac Offline OP
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All sorted had a bad earth at the rectifier running mint. Got a short video of it running but god knows how you upload
Can't wait to get out on the pub bike 😜

Re: Bsa b40 electrical problems [Re: Bigmac] #798238 02/13/20 3:36 pm
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Allan Gill Offline
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Try using Vimeo for video uploading. It’s free and the links should work on here using the β€œfull editor” tab


beerchug

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