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Blowing fuses #781816 08/18/19 2:46 am
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Anza A. Offline OP
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Well I made my first journey to the local gas station with my recently-got-running 68 A65F. Turned out to be a one way trip. Bike died just as I got to the gas station and wouldn’t start. I checked the fuse, which was blown, and thought I’d found the problem. My wife brought me a spare, which promptly blew upon attempting to start. Battery is charged. I’m pretty new to BSAs; any ideas on what I should check once I get it back home?

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Re: Blowing fuses [Re: Anza A.] #781829 08/18/19 8:09 am
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Allan Gill Offline
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Disconnect the zenner diode and try again.


beerchug
Re: Blowing fuses [Re: Anza A.] #781832 08/18/19 8:27 am
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What amp rating of fuse are you using?


Amateur Loctite enthusiast.
Re: Blowing fuses [Re: Anza A.] #781838 08/18/19 11:36 am
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quinten Online Happy
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Still Positive ground. ?
Does the fuse blow only when the key is switched on ?


Wire up a small 12v. light bulb in place of ... or in series ... with the fuse .[Linked Image from w8ji.com]
The bulb will light .. but limit current through to ... wherever the short is .
Start pulling off wire connectors , one at a time till the light goes out .

Some wires that live never the key switch are
1. a white wire for zener ... another white wire to the coils
2. Brown/w white from rectifier
3 ..another brown/w white to the light switch

Last edited by quinten; 08/18/19 4:57 pm.
Re: Blowing fuses [Re: Anza A.] #781842 08/18/19 1:06 pm
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Had a similar situation recently.
Turned out to be a short from headlight switch terminal to headlight.
Try a wrap of tape around the terminal prongs and see if the fuse still blows on turn.


1970 T120R
1970 Commando
Re: Blowing fuses [Re: Anza A.] #781861 08/18/19 4:41 pm
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Anza A. Offline OP
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The fuse was a 35A/17A continuous. Still positive ground, blows the fuse with key off. I’ll set up a light bulb and start looking; thanks for the ideas all!

Last edited by Anza A.; 08/18/19 5:14 pm.
Re: Blowing fuses [Re: Anza A.] #781883 08/18/19 7:58 pm
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As it blows the fuse without anything switched on, the short could be anywhere from battery -ve onwards to the ignition switch.

Put the bulb in place of the fuse as suggested, and it glows, yes?

Then disconnect Zener as Allan said, then rectifier. I would expect the bulb to extingiush at one of these points. They are the most likely failures to cause fuse blowing as you describe.

If it doesn't go out, disconnect the battery power at the ignition switch (either brown/blue or brown/white depending on whether you have ammeter).

Now if the light goes out, the fault is in the ignition switch or onwards.

If the light stays on, the fault is between the wire terminal just detached and battery -ve.

I think you will have located the issue by this stage,pls let us know.

Re: Blowing fuses [Re: Anza A.] #781885 08/18/19 8:33 pm
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Anza A. Offline OP
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Finally got a chance to take another look at it. I connected a bulb in place of the fuse, and discovered that it did not glow with the key off, so I apologize for the incorrect information. I did find through trial and error that if I pull one of the connectors off of the negative side of the right side coil, the light goes out. I was short on time, so I couldn’t trace the wires from the coil. Is there any way the 25+ year old coil could have shorted, or would the short still probably be elsewhere in the harness? Sorry of the simple questions, still pretty new to this bike.

Last edited by Anza A.; 08/19/19 6:57 pm.
Re: Blowing fuses [Re: Anza A.] #781886 08/18/19 8:50 pm
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That coil must be number1 suspect, especially if the light reliably comes on and goes off with repeated connection/disconnection of the feed wire. A multimeter test of the coil would be conclusive. Does it show any signs of crushing by its clamp bracket?
If you can get that wire onto the -ve of the left coil, the light should stay off, as its very unlikely both coils have failed at the same time. This would pretty much confirm right hand coil failure.

Re: Blowing fuses [Re: Anza A.] #781887 08/18/19 8:51 pm
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Yes coils short .
If a "can" coil is overly squeezed in its mounting... it starts to short.
Sometimes it takes time ... sometimes it takes heat .

The can-part should have no continuity to any of the three electrical connections .
Check with an ohmmeter
Or using the light bulb tool .
pull the coil , from its mounting ... still hooked up to the wiring and test light .
And then touch the coil to ground ... light ?
Pull the can from ground conract .... no light ?

You can sometimes wrap the coil in an old. inner tube ... and still use it .
This is a bodge ... but in a pinch ... will get you home

Re: Blowing fuses [Re: Anza A.] #781892 08/18/19 9:13 pm
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If it is a coil I have a set of Lucas 12v Ignition Coil 47276 ordered by mistake. Unused due to the no return policy.
Yours for the shipping if you need them.


1970 T120R
1970 Commando
Re: Blowing fuses [Re: Anza A.] #781897 08/18/19 9:26 pm
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Anza A. Offline OP
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No signs of crushing, but upon further inspection they very well could be original. I connected the wire to the negative of the left coil and the light stayed out. With the wire disconnected, the right coil can had continuity with both terminals, while the left one did not. When I connected all wires, both coils showed continuity from can to terminals. Seems like new coils might be good...

Last edited by Anza A.; 08/18/19 9:28 pm.
Re: Blowing fuses [Re: Hugh Jorgen] #781899 08/18/19 9:41 pm
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Hugh, i believe the 47276 coils are 1 5/8 inch, while mine are 1 7/8 inch. Thank you for the offer though

Re: Blowing fuses [Re: Anza A.] #781930 08/19/19 6:58 am
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if the points are open there should be no light. if the points are closed the light would be on, but it might be something else. take the wire off the coils to double check

Last edited by Mitch; 08/19/19 6:59 am.
Re: Blowing fuses [Re: Mitch] #781941 08/19/19 12:21 pm
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Originally Posted by Mitch
if the points are open there should be no light. if the points are closed the light would be on, but it might be something else. take the wire off the coils to double check


+1, its highly likely that at any point one of the points will be closed, if the igntion is left on it would drain your battery and make the coil very hot!

Have you disconnected the zenner yet? if you cant remove the spade, remove the heat sink and protect it from touching any other part of the bike.


beerchug
Re: Blowing fuses [Re: Allan Gill] #781950 08/19/19 3:08 pm
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Good point , with the ignition on , the 160° points cam almost insures one coil or the other
Is normally recieving power ... and that would light the test light .
This would have to be distinguished from a short through the "can"
...
By Flipping open the points or removing the wire to the points

Or just slowly kicking the bike over .

.

Re: Blowing fuses [Re: Anza A.] #781961 08/19/19 6:56 pm
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Anza A. Offline OP
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I did disconnect the zener diode, the light stayed on. Unfortunately work is interrupting my troubleshooting for a few days, but I’ll check the points and post the results when I get back home. Thanks for all the ideas so far, I probably would have been fumbling around for a week otherwise.

Re: Blowing fuses [Re: Anza A.] #782493 08/25/19 12:55 am
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Anza A. Offline OP
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Well the right coil was shorted between the can and the primary coil while off the bike, so I swapped it with a fresh coil, which fixed the fuse blowing problem. However, I now seem to have developed another issue of the right cylinder not firing. Left plug wire connected by itself and it runs, right one only and nothing. Both spark plugs are firing. I swapped all coil wires from the left coil to the new right one, still ran the left cylinder. Tried different spark plugs. Checked compression again, within 5 psi of each other. Cleaned the right carburetor again. I’m thinking the points might be a bit worn, but I don’t want to throw parts at it. Any ideas what I should check next?

Re: Blowing fuses [Re: Anza A.] #782495 08/25/19 2:46 am
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If you have spark on both plugs then the problem is likely the carb. Have you ever cleaned out the idle passage?

Re: Blowing fuses [Re: DMadigan] #782505 08/25/19 5:31 am
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I was hoping it was the idle circuit, but I removed and cleaned the pilot jet and blew out the passages with carb cleaner and air. There didn’t seem to be any issues there.

Re: Blowing fuses [Re: Anza A.] #782517 08/25/19 7:56 am
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Is the spark as good on the right side as the left? It might be worth cleaning up the contacts in case of any arcing caused from the coil problem.


beerchug
Re: Blowing fuses [Re: Anza A.] #782522 08/25/19 10:02 am
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Quote
I removed and cleaned the pilot jet and blew out the passages with carb cleaner and air


The pilot jet is only 100% cleared out with a 16 thou drill bit, air and carb cleaner do not work on such a small jet.

Re: Blowing fuses [Re: kommando] #782529 08/25/19 12:21 pm
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Originally Posted by kommando
Quote
I removed and cleaned the pilot jet and blew out the passages with carb cleaner and air


The pilot jet is only 100% cleared out with a 16 thou drill bit, air and carb cleaner do not work on such a small jet.



Absolutely. do you have a #78 drill? is it an early Concentric with the pilot jet in the float bowl roof? After 68 the pilot jet was located behind the mixture screw and is not a removable item.

if it is a 68 carb consider changing the main jet holder and jetting to the later 69 or 70 settings, the 68 was the first year of the conc on A65s and they didnt get it quite right. The pilot jet in the bowl roof was moved because on some Triumph twins it gave very poor running,

Last edited by gavin eisler; 08/25/19 12:26 pm.

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Re: Blowing fuses [Re: Anza A.] #782553 08/25/19 4:35 pm
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To clarify it would/could cause the engine to die when shutting off throttle because of a surge on the jet and the distance the fuel had to travel. Moving the jet closer to the welch plug solved this issue. When I first built my lightning I had the 68 style pilot jets (I had the other jets as per the manual but in 4 stroke version, not 2 stroke) I also suffered the problem as above. I sent my carbs back to AMAL and they fitted the bush jets.


beerchug
Re: Blowing fuses [Re: Anza A.] #782588 08/25/19 10:00 pm
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Interesting, I will look into 69 and later jets. The current right side pilot jet (screw in) is very clean, and the pilot circuit is clear. The left cylinder is running great. When I try to start on just the right side there’s really no evidence of a spark, though the spark plug is sparking. I cleaned off the points, but I still wonder if anything else got damaged when the coil shorted out. When running with the point cover off the lower points/right side appears to make a much more visible spark than the other.

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