bsa b25 starfire blowin fuse 1970

[abiteachuck]

Hi, everybody ive just joined, so thanks for havin me.
i just bought this bike 95% finished, but i cant seem to sort out the fault.
the bike is + earth, whats happening is when you try to start it it blows the fuse the has burnt out a set of points.the reason must be the feed is perminent live so every time the points close it creates a dead short, any help will be greatful,hope i have made it clear.
thanks keith.
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They dont make um like this any more.

[Paddy Blake]

I am not sure but I think there should be a wire from the points to a condenser then from there to the HT coil.
Is there a condenser in where the points are.

[abiteachuck]

thanks ya there is a condenser and its wired to the same wire that feeds the points it comes from the + side of the coil
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They dont make um like this any more.

[Paddy Blake]

That sounds wrong.
I will have a quick look for a wiring diagram for close to that.

Have a look here to see if there is something with points that may help you.
https://www.bikechatforums.com/viewtopic.php?p=2322761#2322761
I have to go.

[stinkwheel]

Scorched/burned points are a symptom of a duff condenser.

It would have to be totally mangled to give a dead short though. Even if it was, you should still have enough resistance in the primary windings to prevent a fuse popping. The coil might get pretty hot though.

I suspect you have a short circuit™* in the wiring leading from the points to the ignition coil or an internal short in the primary windings of the ignition coil.

A duff/disconnected zennor could also lead to fuses blowing (due to excess voltage) but only when the engine is running.

I did a wee sketch of an ultra basic points iginition system (not included ignition switch and fuse).

* "Short circuit" is a trade mark of the LUCAS Electrical Company. Patent No: 1562329A6
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Odie]

Problem is with your understanding of the markings on the coil.
The + is not positive but power feed in (- in + earth bikes) and the - on the coil goes to the points.
+ = power in, - = low tension
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You are so ugly when you were born the doctor said "I?m gonna drop it, if it falls is a rat, if it flies is a bat."

[abiteachuck]

[abiteachuck]