Bonny into Bonfire (well nearly!) (1967 120) - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 6 (permalink) Old 05-15-2019, 07:42 PM Thread Starter
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Bonny into Bonfire (well nearly!) (1967 120)

Fitted a new battery so i went for a test ride, i had ridden about 20ks pulled over and switched off for about a minute or so, started the old girl up and pulled away to a fairly large bang/back fire and large puff of smoke. Turns out the positive wire from the battery to the frame had completely melted away. I called a friend out who replaced the wire (with a slightly thicker gauge as the other was a bit thin) long and short of it was it started up fine but when i went to pull away (higher revs) it did the same not only completely melting the wire like a fuse it actually fused the copper together in places. we got it back to his place and measured the (tri spark) regulator and it seemed to be faulty. Purchased a replacement regulator (and added a fuse between positive and frame, even though there is a fuse between negative and wire loom which never blew) and fitted and shed started up but wouldn't tick over, but revved fine, so i upped the tickover screws to keep her running, but the trouble is now she just doesn't run right. I rode it for a short run and the tickover is all over the place, sometimes it's OK and then revs up too high, i guess my upping the tickover screws keeps her running in the faulty state but then something starts to work/kick in OK and tickover goes up to high.
Do you think its just a coincidence that something else has gone in the mean time as the initial bang/back fire was pretty loud?
Can a battery (to high cranking amps perhaps ?) cause weird problems as only happened after i fitted that?
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post #2 of 6 (permalink) Old 05-15-2019, 08:18 PM
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You hooked it up the right way, I hope ? Positive earth. Too “big” of a battery shouldn’t cause any issue, as long as when you close the seat it isn’t touching the terminals. Remember, clearance will diminish with your weight on the seat. A big bump can cause contact, especially if the battery isn’t tied down. Maybe if the voltage regulator went bad it damaged the battery. I glue a strip of rubber on the bottom of my seat over the battery area . You can use a piece of modeling clay to check clearance.
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post #3 of 6 (permalink) Old 05-15-2019, 08:56 PM
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What amp fuse are you using? I know the manuals say 35 but that is a British rating. You need to use a 15 US rated one.
Symptoms sound like the ei is getting intermittant or low current. Definitely an electrical problem given the recent history. Melted contacts in ignition switch? Shorting to ground somewhere in the system? Not familiar with a Trispark. On a Boyer or Pazon you would run a hot wire from battery negative to the hot lead on the ei box. If the bike runs well then you know you have a problem somewhere in wiring or switches.

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post #4 of 6 (permalink) Old 05-15-2019, 09:27 PM
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Seems lie a good time to pull out the old Voltage or multimeter and have a poke around to confirm you've got 12-12.8v at battery, then see how that changes with rpm. Also check for AC leaking into the system past the Reg/Rec. Hows the 12v feed to the EI? You may have damaged the EI (explaining the poor running) with the firing of the positive lead if there was some kind of short happening.

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post #5 of 6 (permalink) Old 05-16-2019, 04:01 AM
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What battery did you fit?
What condition is the seat base in?
Is the seat fitted with the rubber grommets that hold it off the frame?
How did you conclude the reg was faulty?
Can you post a pic of the under seat area?

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post #6 of 6 (permalink) Old 05-16-2019, 04:27 AM
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If you read the Britbike internet forums, sadly, this is a regular occurrence. However, it wouldn't have happened on your bike if it had the original wiring harness or a well-made replacement; sadly it has a crap replacement (Wassell "Genuine Lucas"? ).

Risking telling you something you understand already, the standard "positive ground" of your bike's electrics simply means the metal parts of the bike's structure - frame, engine, bodywork, etc. - are connected to battery positive.

The snag with then putting just one single fuse in the wire attached to battery negative is it doesn't protect against all possible short-circuits, including the ones your bike has just experienced/is experiencing.

The shorts on your bike are almost-certainly something metal touching both the battery negative terminal and an aforementioned metal part of the bike's structure, a/the fuse in the wire attached to battery negative won't blow, because the shorts aren't through a/the fuse there.

The only thing that protects against a short from the battery negative terminal itself on any 'positive ground' bike is a fuse in only a single wire actually attached to the battery positive terminal. This also protects against all the possible short-circuits that a fuse in the wire attached to battery negative protects against.

Your bike's original wiring harness, or a well-made replacement, would've had the single fuse in a single wire attached to battery positive.

Other things to check on your bike now:-

. What is/was touching the negative terminal of the new battery, as your post starts off "Fitted a new battery" ...

. Fuses:-

.. If you're using standard automotive blade fuses, neither the new fuse in the one single wire now attached to battery positive nor the fuse in the wire attached to battery negative exceeds 20A, better is 15A.

.. Otoh, if you're using tubular glass fuses with metal end caps, check the rating very carefully - 'British' should be 35A (unlike all the others, it's a 'blow' rating, not a 'continuous' rating ), US/Japanese again shouldn't exceed 20A, better is 15A.

A simple mod. you might want to consider now - '68-on, the battery sat on a rubber mat (82-8091) in the bottom of the carrier; buy one and fit it over the top of the battery, held in place by the standard "Retainers".

A second mod. for the future - an educated guess says you've been sold the 'standard' 9Ah (Amp-hours) replacement battery 'recommended' for most Britbikes with 12V electrics. Next time you buy a replacement, consider buying the similar 7Ah one - has the same length and width but is a little shorter. Btw, (cold) "cranking amps" (ccA) has absolutely nothing to do with anything on a kickstart-only bike.

Originally Posted by madtothemax View Post
measured the (tri spark) regulator and it seemed to be faulty.
Depends how it's connected to the harness but unlikely to be anything to do with the original problem; however, could be buggered now. Post how the new regulator is connected.

Originally Posted by madtothemax View Post
now she just doesn't run right.
Points or electronic ignition? If electronic, make/model?

'Fraid the new battery could be buggered - you've shorted it twice, shorts draw a huge current from a battery, the battery is relatively small and easily knackered by heavy current draw it was never designed to supply.

Measure across the terminals with a Voltmeter, if the meter shows less than ~12.5V, put it on an overnight trickle-charge.

After an hour or so off-charge, measure across the terminals again; if it still shows less than ~12.5V, it's buggered (consider my advice for a smaller replacement battery?).

Otoh, if measuring across the terminals shows the desirable ~12.5V, connect it to the bike's electrics, connect the meter across the terminals, watching the meter:-

. first turn on just the ignition, meter might just a little lower but it shouldn't be much (if the meter indicates 12V or lower, battery's buggered);

. if the meter is still indicating ~12.5V, turn on the lights including the headlamp; again(if the meter indicates 12V or lower, battery's buggered.

The above is just a quick-'n'-dirty load test, only definitive if the battery fails; if it 'passes' unfortunately it doesn't necessarily mean the battery is 'good', still have it properly load-tested by an auto-electrician with the kit.

The other area to examine carefully is the wiring harness itself; regrettably, other Red 'ground' wires within the harness might've been damaged by the shorts.

Hth; post how you get on?



Last edited by StuartMac; 05-16-2019 at 05:46 AM.
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