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I think the battery is the culprit. 10 months ago I had the same problem with the bike firing on one cylinder, I did mange to ‘move’ the problem to the other cylinder by swapping coils (resulting in replacement) but I think the real cause was the low battery voltage.

12.5v is pretty flat, it might look healthy again after a good charge but once under load the voltage will drop quickly. Below is an extract from the thread I started, mine got down to 11.35v with this testing and I think yours will do something similar. The new replacement battery I have starts at around 12.9v and doesn’t drop below 12.7v

“The battery voltage when installed was 12.71 dropping to 12.56 when I switched the ignition on. Five minutes later I tested again, at ignition off the battery was still at 12.56 dropping to 12.41 with the ignition on. Once it was stable there I switched the headlight on for 30 seconds, this took the voltage down to 11.35. Headlight off but ignition still on it recovered to 12.24. I then switched the ignition off and the battery recovered to 12.41.

So in ten minutes of testing which included 30 seconds of the headlight being on the battery lost 0.3v from its starting point of 12.71. Knackered do you think?”
 

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Going in the 11 volt range is getting shaky, I think. But when it’s a kick start bike , I’ve used worse as long as it’s holding a charge and the charging system is functioning ok.
 

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Discussion Starter #23
Hmm, I did a quick battery test on my way out this morning. Ignition and headlight on for ~1min dropped the voltage by ¼ - ½ V, so it was reading 12V after this brief test. I'm inclined to replace the battery cause I'm running out of ideas pretty quickly.

Rusty1: Interesting to hear that you also had a one cylinder misfiring issue and turned out to be the battery. Fingers crossed this is the same issue I'm having.
 

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Hmm, I did a quick battery test on my way out this morning. Ignition and headlight on for ~1min dropped the voltage by ¼ - ½ V, so it was reading 12V after this brief test. I'm inclined to replace the battery cause I'm running out of ideas pretty quickly.

Rusty1: Interesting to hear that you also had a one cylinder misfiring issue and turned out to be the battery. Fingers crossed this is the same issue I'm having.
Yes I think you need to replace it anyway, 12v after that brief test is very poor assuming it was fully charged to begin with. The conclusion I reached was that my ignition system has an imbalance somewhere which would never show itself with a healthy battery. Only when the voltage became marginal did this show up, one plug failing to spark before the other one did.
 

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Hi Neal
I’m not sure it did so badly, it was a quick stress test of the battery under headlamp load, it did not fall away to 10V or anything extreme.
Hopefully Stuart will comment on the battery, he is a master at voltage analysis.

If theBoyer started to misbehave due to low voltage, it should affect both cylinders.

One thing that might be of interest is the coil voltage and connections, if you have the Lucas or lucas style coil, were they changed to 6V units when the Boyer was installed. Also the wiring of the coils, in case one is wired backwards.
Lucas 6v coils will be marked 17M6 on the bottom, original points 12v coils will be marked 17M12. It is considered good practice to fit 6V coils when using electronic ignition, even though the engine will run on 12V coils.
If they are not marked you can test them with a multi meter
Between the two terminals, ignition off
12v 4-4. Ohms
6v 1.5-2.2 ohms

also check the wiring to the coils,
Black wire of Boyyer to coil 1 neg terminal,
connector wire between coil 1 pos terminal and coil 2 Neg terminal.
Coil 2 Pos terminal connected to Boyer red wire and battery Pos terminal.

This is worth a check as the spark will be weak if wrong, but An EI problem will affect both cylinders, so a fault here does not match your symptoms.

regards
Peg
 

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Hi,

Stuart
is a master at voltage analysis.
Errrm ... <koff> <shuffle> ... thank you, although I'm pretty sure "master" overstates my knowledge ...

Nevertheless, the actual figures in:-

12.5v is pretty flat,
The new replacement battery I have starts at around 12.9v and doesn’t drop below 12.7v
... are likely to be the meter over-reading ...

The chemicals that make up a lead-acid cell ('wet', AGM, gel, etc.) give a potential difference of 2.1V when fully-charged, so the six cells of a nominally-"12V" battery should measure 12.6V fully-charged. Then 12.3V is partially-discharged, actual 12V is a very low charge and <12V is badly-discharged or shagged.

The first way to tell between shagged and discharged ("part-", "very low" or "badly-") is to trickle-charge the battery for about ten hours - reason for ten hours is the charge shouldn't exceed 1/10th of the battery's Ah (Amp-hour) rating; e.g. a standard non-electric-start Triumph (most Britbikes) battery is 9 Ah, it shouldn't be charged at more than 0.9 Ah. Having trickle-charged the battery for about ten hours and then left it unconnected for another hour or so (to allow any 'surface charge' - that gives a falsely-high Volts reading :( - to disperse), the unconnected Volts should be the aforementioned 12.6V. If they're lower, you can be pretty sure already the battery's shagged. :(

If the battery's measuring 12.6V after trickle-charging and standing, the second way to confirm it was simply discharged is to connect it to the bike's electrics, connect the meter across it and observe the meter readings as various things are switched on:-

. Everything off should show the same reading as unconnected.

. Ignition only switched on should barely change the reading. With many (but not all :rolleyes:) Boyer-Bransden e.i., any drop in the meter reading when it was switched on should change back to the original reading when the B-B does its 'power down when engine movement not detected. Same applies to any other e.i. that has the same party trick ... :(

. Similarly, all lamps except headlamp switched on (with or without ignition) should barely change the meter reading.

, Switching on the headlamp, the meter reading should drop. But, given what I've written above about a drop from 12.6V to 12.3V indicating a part-discharged battery, the meter across a 'good' battery shouldn't show that big a drop just when the headlamp's switched on (assuming the "headlamp" isn't a couple of 100W-main-beam bulbs ... ;)).

. Finally, you should be able to leave all lamps switched on, including standard or 60/55 headlamp bulb, engine not running, for a good half-an-hour and a meter across a 'good' battery shouldn't drop below actual 12V. If the battery will only last a quarter-hour or so, it's OK but you want either to test it with a proper battery load tester, or have a proper auto-electrician do it, and budget for a possible replacement.

battery test
Ignition and headlight on for ~1min dropped the voltage by ¼ - ½ V, so it was reading 12V after this brief test. I'm inclined to replace the battery
Apart from I don't like to simply replace an electrical component without being as sure as I can be that replacement will fix the problem, I'd simply want to confirm a shagged battery with a proper load test while budgeting for a likely replacement ...

Between the two terminals, ignition off
12v 4-4. Ohms
6v 1.5-2.2 ohms
When 'original Lucas' made the coils, "12V" could measure between 3 and 4 Ohms, "6V" between 1.5 and 2 Ohms, Lucas coils tended to measure pretty-much in the middle of the range (i.e. "12V" 3.5 Ohms, "6V" 1.8 Ohms), it's only pattern and 'Wassell Lucas' coils that can measure higher resistances (which isn't a good thing :().

I'd also check:-

. between each coil LT terminal and the coil's HT terminal, the meter should read ~5,000 Ohms on a 'original Lucas' coil;

. between all terminals on a coil and the coil's case, the meter should read tens of thousands of Ohms (some meters display the infinity symbol - looks like an horizontal "8").

Hth.

Regards,
 

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Discussion Starter #27
Hi Peg and Stuart,

Ran the above tests:

Between the two terminals, ignition off
12v 4-4. Ohms
6v 1.5-2.2 ohms
I have the Lucas 6V coils. They both read a little bit lower: 1.3 Ohms. Between the HT and LT connection reading 5K Ohms, and between the terminals and the coil case is infinity.

also check the wiring to the coils,
Black wire of Boyyer to coil 1 neg terminal,
connector wire between coil 1 pos terminal and coil 2 Neg terminal.
Coil 2 Pos terminal connected to Boyer red wire and battery Pos terminal.
Wired as indicated

The first way to tell between shagged and discharged ("part-", "very low" or "badly-") is to trickle-charge the battery for about ten hours
Had it on the charger last night in fact. Reading today was 12.6V after about 1 hour disconnected from charger. That appears to be correct. Turning on ignition did not drop the reading. Turning on headlamp dropped ever so slightly.

leave all lamps switched on, including standard or 60/55 headlamp bulb, engine not running, for a good half-an-hour and a meter across a 'good' battery shouldn't drop below actual 12V.
Reading was about 12V - 12.3V (I have an analog meter with not the best precision so tough to say exactly) after 30 min of headlight and ignition on. After the test, I checked again 30 min later and battery had recovered to north of 12.5V.

sigh feel like I'm back at the drawing board again...I dunno, maybe I should replace the battery cause it still is 5 years old and that would at least confirm that it's not the battery, especially since rusty1 reported the same one cylinder misfire that was remediated by a new battery.
 

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My Boyer will work as long as i have a battery fitted and often shows just 12 volts after a lay up. I had run my T120 on 12 volt coils for 20 years and had some firing on one cylinder starts. When i decided to find the issue, it was a faulty plug cap and i also fitted a pair of 6 volt coils which have transformed my starting up. The only time my Boyer plays up is if the battery disconnects or my alternator stops charging and the voltage goes down a lot. I notice lunmad video shows his bike running with voltage below 8 volts which would seem impossible. John showed this in detail just to prove a point about low voltage issues.
I know if my battery is failing to charge as when it gets very low and i use indicators, the engine cuts out at each flash. A real bucking bronco ride.
 

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Hi Neal,

I have the Lucas 6V coils. They both read a little bit lower: 1.3 Ohms.
Hmmm ...

Which "Lucas" - "original" or Wassell?

If "original Lucas", are the coil casings anodised blue? 'Back in the day', original Lucas made what it called "sports coils", 12V were red and 6V were blue, both 'Voltages' had a slightly lower primary resistance than the corresponding silver-case coils; the cod-science was they'd charge quicker at high rpm; in reality, I've known normal silver-case coils sparking/charging quite happily at rpm wa-aa-ay higher than any Britbike engine can manage without turning itself into a 3D version of the parts book illustrations ... :sneaky:

If your bike's Boyer-Branden e.i. is analogue (Mk.3/4), according to at least part of the half-arsed "General Data" in the fitting instructions, two 1.3-Ohm-primary-resistance coils are too low:-

. The primary resistances of individual coils connected in series are cumulative; i.e. two 1.3-Ohm resistances total 2.6 Ohms; according to the B-B destructions, "Total Ignition coil resistance should be a minimum of 3.5 Ohms". (n)

. Otoh, the preceding sentence in that same section says, "The maximum ignition coil current through the unit must not exceed 5 amps"; which it doesn't even with 2.6 Ohms (the relationship is Ohm's Law - E=IR or Volts = Amps x Ohms; 12 Volts and 2.6 Ohms equals only 4.6-ish Amps). (y)

... so I'm dubious about advising buying new coils, when they'll be 'Wassell Lucas' and might not fix the problem ... :( Can you first borrow and connect a pair of '6V' coils with a more-normal primary resistance, to see if they fix the problem?

maybe I should replace the battery cause it still is 5 years old and that would at least confirm that it's not the battery.
Hmmm ... again. Personally, I'm not a fan of throwing money at an entire system with a problem, hoping just the money will identify the problem component. However, it isn't my money you're spending ... :)

Also ime, a 5-year-old battery that's been maintained reasonably well should have several more years' life on a non-electric-start bike. But the operative phrase is, "maintained reasonably" - kept topped-up, kept warm and trickle-charged regularly when the bike isn't used for lengthy periods.

Regrettably, the 'load test' you've done is only partially-reliable :whistle: - if the battery fails, it's knackered; however, if the battery 'passes', it only means the battery's less-likely to be the problem in a system, not that it's definitely 'good'. If I'm still suspicious of a battery that 'passed' the quick-'n'-dirty load test, I haul it to a proper auto-electrician for a proper load test before condemning/replacing it.

Hth.

Regards,
 

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Discussion Starter #30
Hi Stuart,

Which "Lucas" - "original" or Wassell?
My mistake, they are actually PVL 6 volt coils. I thought I recalled Lucas, but I popped one out to double check just now. Sorry bout that. They look just like these: 45275 - 6V - Germany

If your bike's Boyer-Branden e.i. is analogue (Mk.3/4)
Yup, it is the Mark III model.

Can you first borrow and connect a pair of '6V' coils with a more-normal primary resistance, to see if they fix the problem?
Sadly, I don't know anyone that has an extra set of coils I could borrow around where I live. I did try swapping which coil fires which cylinder, but that did not resolve anything.

If I'm still suspicious of a battery that 'passed' the quick-'n'-dirty load test, I haul it to a proper auto-electrician for a proper load test before condemning/replacing it.
Yea, I'll do that. A local auto parts shop has a free battery tester. I'll see if I can get that done today or tomorrow.

Thanks for the suggestions.

Neal.
 

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Back in the day when I rode a 1973 T100P I had starting problems following a top end refurbishment. The bike would run and then die.

A bike mechanic friend of mine ran a series of tests to locate the problem, gave up and then finally started to strip the engine down. Once he removed the carb, he discovered the problem.

Turns out that when I reassembled the carb and the inlet manifold, I put one of the gaskets on the manifold on upside down, not noticing that they were an off centre oval shape.

This has the effect of restricting air/fuel mixture to one of the cylinders.

Specsavers weren't a thing back then - pity.



Sent from my SM-G950F using Tapatalk
 

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Discussion Starter #32
Was able to pop over to the auto parts store today....per their testing, battery is bad and should be replaced. So I'll plan on doing that as a matter of course.

Turns out that when I reassembled the carb and the inlet manifold, I put one of the gaskets on the manifold on upside down, not noticing that they were an off centre oval shape.
Peg also suggested that I do a leak test on intake manifold. Once I get the new battery and it fire the bike up, if it is still misfiring I will check this.
 

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Hi Neal,
I suggested the battery check because you said that the cylinder would start to fire as the revs increased, although I would associate this with a carb fault normally as the fuel starts to get metered by the slide/needle jet/main jet and not the pilot jet, I wondered if the voltage rise from the alternator charging was allowing the cylinder to fire at higher RPM. I still consider it a long shot.
The same with the coils, 12v coils reduces the spark strength. But you had 6v coils so that was good, the coils were wired the correct way so the sparks were firing from the hot centre electrode to the cooler outer shell, and not the other way around.
I was wondering if a high resistance on the connecting lead between the two coils could lower the voltage to one of them. You did swap the leads on the plugs though without the fault transferring to the other side.
Did you swap your new spark plugs, I have known new plugs to not work before. It seems there are a lot of snide NGK plugs being sold these days.

Arthur Conan Doyle wrote for his great detective Sherlock Holmes- When you have eliminated the impossible, whatever remains, however improbable must be the truth.

We seem to have a lot of impossibles, loads of improbables and just cant find the truth.

regards peg
Got my fingers crossed that the battery helps.
 

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Discussion Starter #34
Hi all,

Sadly the new battery did not resolve this issue. I also did a more thorough inspection of the valve train and checked the lash and everything looks good.

At this point, I am officially out of ideas. To recap what has been suggested/done to this point:
  • Cleaned pilot jets, checked air screws, throttle stop positions, cables, etc. Swapped carbs side-to-side, no difference.
  • New fuel.
  • Checked coils, plug, wires, battery. Swapped spark plug cables side-to-side (but leaving on same coil, so the coil fires the opposite cylinder), no difference. New spark plugs and new battery, no difference.
  • Mechanical inspection, valve clearances, compression check. All okay.
Either I'm missing something obvious, or this is a very strange fault to diagnose. I do wonder if it is electrical. Could somehow an inbalance in the system leave the left cylinder to not fire? Wouldn't swapping the spark plug cables check this, since they are the point closest to the spark?

Any long shot ideas before I take this to a bike shop?

Neal.
 

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I'm really sorry that my suggestion of the battery being the culprit wasn't correct Neal. Looking at what you done I can't think of anything else that would cause the issue and would be hesitant to suggest anything involving more cost.

Edit: Have you tried removing the plug leads from the coils and swapping them over leaving them on the same plugs?
 

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Discussion Starter #36
No worries, apparently the battery was going bad anyway, at least according to the auto shop that did the test.

Have you tried removing the plug leads from the coils and swapping them over leaving them on the same plugs
Kinda...I swapped the spark plug cables at the spark plug end, not the coil end. It didn't make a difference.
 

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Kinda...I swapped the spark plug cables at the spark plug end, not the coil end. It didn't make a difference.
Yes seemed daft I know, was just thinking of all the combinations of the HT lead/coil/plug cap swaps before you take it to the shop. Might be worth swapping the entire lead & plug cap from one side to the other?
 

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Discussion Starter #38
Certainly am willing to try that! Will report back tomorrow.

Also, re:
hesitant to suggest anything involving more cost
If I have to take this to my bike mechanic will cost me much more than randomly replacing a few components, if it can lead to a diagnosis, so suggest away.
 

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Hi Neal,
Swap your new plugs just in case, measure the resistance in the lead between the plugs, or measure the voltage at each coil with the ignition on.
Both of these are long shots, but worth trying.

you swapped the ht leads at the correct end to check everything,( coils/HT leads/plug caps.)

If the misfire is proving to be immovable, then maybe it is in an immovable part of the engine,
Inlet tract, —leaks or blockage
cylinder, -valve leaks, ring leaks, cylinder head gasket
exhaust - blockage if not a crossover type.
Regards
Peg.
 

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Hi Neal,
What brand / number spark plugs are you using? Have you still got the "old" plugs that were in the engine before you made your changes? If yes, could be worth fitting them to see if any better. I put a set of brand new Champion N3 in my '77 T140, within a couple of hundred yards, bike went onto one cylinder. Found one plug just would not spark. I assume there must have been an internal fault that made the plug fail completely.
Another clutching at straws idea. I think you have tried everything, judging by the suggestions posted earlier. Could you try connecting the white Boyer box lead direct to the battery? I am assuming your machine is positive earth, so connect direct to battery negative. Only issue with this, is that you will have to break this connection to turn engine off.

Hope you soon have this sorted.

Andy
 
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