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Discussion Starter #1
Hi all,

The last couple of times I have ridden the T140V when hot outside (>90 degree weather) I have had an issue develop about 15-20 min into the ride. Up until that point, no issues. But once the engine starts getting quite hot, it begins to stutter when I crack the throttle 50% or more. Happens in all gears.

The first time it happened, I checked the spark plugs to see if they could tell me anything. They were bone dry, but not obviously discolored. The carbs were hot to the touch (yes, I have the thick o-ring in place).

I searched through the forums here and that led me to think perhaps the bike was running a bit lean leading to overheating, so I adjusted the pilot screws in about 1/4 turn. It helped, but only by prolonging the time it took until this happened again.

I'm leaning towards the fuel still being too lean leading to overheating. Problem is I don't have a choke on the bike to confirm. I could keep trying to richen the mixture (turn air screw in some more, or move the needle clip down a position).

First question: is it safe to ride till I get this sorted out? I don't want to hole a piston.
Second question: is there a better way to diagnosis this then just to "assume" it is too lean, and focus on carb settings?

I am also thinking of putting some phenolic spacers between the manifold and head to try to block some of the heat coming off the cylinder, but that seems to be treating the symptom not problem.

Thank you.
Neal.
 

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Hi Neal, The phenolic spacers won't help. Trust me on this.

Pilot screws will have minimal effect once you are much above idle.

Absolutely you want to correct this soon as possible. Don't ride in the misfire zone unless you are doing diagnostics. Then do minimum as possible.

Always verify your voltage is good from battery + to EI power wire or coils if using points. Measure this hot when bike is acting up. Carry volt meter in your back pack.

Mark your throttle.

Print this & road test. We'll go from there.


My bike has a choke, I could never find lean by applying choke. I know some can, but I certainly couldn't. The tuning guide gets into telling lean by backing off throttle slightly, like 1/32 throttle & feeling if power slightly increases.

Generally lean is worse colder & better as motor heat soaks. Online it's hard to tell. Road testing with tuning guide will teach you a lot. Do you know what 8 stroking sounds like? Rhythmic misfire ah ah ah ah ah. I had to go extra rich on main jet to discover it. Then do 1 size smaller at a time. Lean does not rhythmic misfire. It will feel like loss of power or no enough power as should be.

Of course all tune up items, valve adjustment, timing. No air leaks. Make sure the crossover pipe is good & there is a bolt in the old choke bracket hole or that's an air leak.

Don
 

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Hi Neal,
The last couple of times I have ridden the T140V when hot outside (>90 degree weather) I have had an issue develop about 15-20 min into the ride.
once the engine starts getting quite hot, it begins to stutter when I crack the throttle 50% or more. Happens in all gears.
is there a better way to diagnosis this then just to "assume" it is too lean, and focus on carb settings?
You have checked HT leads are making good contacts with coils and any separate plugs caps?

Have you tried a new pair of plugs?

If yes to both, use the John Healy Initial Diagnosis method:-

. mark the twistgrip housing (dab of black paint?) where you can see it when riding;

. mark the twistgrip beside the housing with four marks corresponding to 1/4-, 1/2-, 3/4- and full-throttle;

. go for a ride; if/when the misfire develops, note the rpm and twistgrip position; change gear; if the misfire persists, note the new rpm and twistgrip position:-

.. if the misfire occurs at the same twistgrip position, the problem is more-likely carburation (same part of the carbs. in use);

. if the misfire occurs at the same rpm, the problem is more-likely electrical.

thinking of putting some phenolic spacers between the manifold and head
While they're exactly how Triumph treated the symptom/problem on some models, your bike's carb. mounting studs aren't long enough for any meaningful phenolic spacer thickness and, if the carbs. are connected to the standard air filters, you'll give yourself problems reconnecting everything. (n)

'73-on, Meriden used a different carb.-head insulation method: your bike should have stepped (1/4" / 5/16" OD) carb. mounting studs and there should be a "Cup" washer and "Insulating ring" between a carb. and each 1/4"UNF self-locking securing nut.

Most importantly, there should be a thick O-ring between each carb. and its manifold. Unbelievably, 😤 the part number for this thick O-ring was misprinted in parts books for years - the Triumph 70-9711 part number is correct, the Amal 622/101 number is not - that's a common thin Amal O-ring, the thick O-ring is peculiar to 750 twins with Mk.1 Concentrics. "Bungling incompetence" doesn't even begin to cover such a long-time mistake and, when you consider what passes for many "Triumph spares dealers" these days ... :rolleyes:

What should happen with all the relevant parts is: even when the 1/4" carb. securing nuts are tight against the 1/4" / 5/16" step in the studs, there should be a gap between carb. and manifold, that's the 'insulation' to prevent heat being conducted from head to carb., the gap sealed by the thick Triumph 70-9711 O-ring.

However, if you (or a PO) has inadvertently fitted thin Amal 622/101 O-rings, while they'll seal between carb. and manifold, there won't be any heat conduction-preventing gap. :(

Hth.

Regards,
 

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Discussion Starter #4
Thanks for the quick replies Don and Stuart.

Good point re: fresh plugs -- I will try that first. Will also double check common sense things like battery voltage, plug and coil connections, etc.

Both referred to the Healy method: I have that guide already. Will start there and run the test as Stuart described. That seems quite clear to me to help narrow down carb or electrical.

Don, I have no idea what eight stroking sounds like. I found a nice description in text, but I would of course like to hear the sound. Couldn't find anything on YouTube. The engine does change sound when the problem happens, and there is a loss of power. Feels more choppy then a consistent loss.

Neal.
 

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Eight stroking will happen at half throttle if the main jet has unscrewed in one carb. Probably not your problem as it happens after 15 minutes.
 

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Look carefully at the high tension spark plug leads. If they are old you could be having "leakage" to ground and this would like be made worse by high temperature. With poor HT leads, you'll get missfire at large throttle openings because the cylinder charge is more dense and if the spark voltage is weak, the plug won't fire.
 

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Thanks for the quick replies Don and Stuart.

Good point re: fresh plugs -- I will try that first. Will also double check common sense things like battery voltage, plug and coil connections, etc.

Both referred to the Healy method: I have that guide already. Will start there and run the test as Stuart described. That seems quite clear to me to help narrow down carb or electrical.

Don, I have no idea what eight stroking sounds like. I found a nice description in text, but I would of course like to hear the sound. Couldn't find anything on YouTube. The engine does change sound when the problem happens, and there is a loss of power. Feels more choppy then a consistent loss.

Neal.
Hi Neal,
one point i will add to the as usual good advice from Don re the trouble people have always had understanding what the term 8 stroking refers to and sounds like is one that myself and anybody that has ever got into jetting hi performance 2 strokes i think understands far easier and quicker due to disastrous consequences of getting it wrong that will result in seizures that more often than not occur after backing off after long WOT and being too lean. A lightening fast clutch hand is your only hope and one i developed real quick as i raced 125cc GP class bikes that with those skinny wee tires put you on your butt real fast.

Why i bring 2 strokes in is i think it will assist those that still not understand the same condition, is now referred to as 4 stroking and i think more pronounced making it easier to know the instant you have reached the desired over rich condition you wanted intentionally as your start point to get main jet right.

So now you can start going one size at a time down until you find the ideal colour you want on the plug
The term used i now becomes obvious because instead of a 2 stroke firing every time thru TDC it is now only firing every 2nd time .
So obviously same condition on a 4 stroke that normally fires every second time passing thru TDC is npw only firing every 4th time hence the term 8 stroking.
But i gotta say i like Don:s phrase "rhythmic misfire" he uses to get across what the condition sounds like and sure to use that in the future.
.
A thought just came through that i will finrsh with.
Anybody that has particularly a chainsaw but mower etc just as good long as it has easily adjustable high speed fuel screw where you will recreate the condition easy as by slowly winding screw out and thus richening the mixture with WOT (wide open throttle) that i always find with no load is what i want.
Aah now i can hear multiple pennies dropping i hope. If not sorry i give up. :D:cool:
 

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Discussion Starter #9
Thanks motomic and DPE. Vapor lock did cross my mind, especially given the hot carb. But it was not hot enough to vaporizer fuel in carb -- I was able to easily restart -- plus I already have the carb standing proud of the manifold with the thick o-ring. I live in a city so to get to good riding roads I have to traverse ~15 min of heavy stop and go riding and the bike tends to get very hot those days when it is >90 degrees.

I placed some new plugs and checked the spark plug wires and will be trying the Healy method that was proposed hopefully this weekend. Will report back whether it is RPM or throttle position dependent.
 

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Discussion Starter #10
Hi all,

Update: ran the "Healy" test today. I had new plugs and a fully charged battery. First off, riding conditions were extremely warm >95 degrees outside. The fault developed sooner than previous times, about 5 minutes into ride.

The fault consistently developed starting around 1/3 throttle opening regardless of engine speed. The best way to describe it is a hesitant feeling in the bike under acceleration. It wants to accelerate (and will jump forward a little bit) but then it just gets held back.

Towards the end of the ride, the bike was running really rough, and it wanted to quit at stop lights. Only way to keep it going was to keep a little throttle at all times. When I got home and let off throttle, bike sputtered and died. Carbs were very warm to the touch, so vapor lock may have been the straw that broke the back. Keep in mind I have the thick oring in place with the "air gap" between the carb and manifold. So if they are getting too hot, may be because the engine is getting waayyy too hot.

Pulled plugs and they were dry, a little bit tan in color, so perhaps a lean condition getting engine to overheat? I am thinking carb problem, or perhaps timing. I haven't done anything that would affect timing settings though, so not totally sure if that fits. Thoughts?

Neal.
 

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It’s a long shot, but could you be getting fuel restriction from the tank. Not getting enough fuel through when needled ?
 

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Hi DPE, That is not a long shot, it needs to be checked. Also fuel cap vent must be checked.

Neal, Check gas cap. Blow into the tiny vent hole on top. It's small, but should freely pass air. Blast some carb cleaner through hole if needed & blow more. Compressed air works good too.

Check fuel taps & banjo filters. At the same time remove bowl drains, turn on fuel tap & observe for free flow out drain holes.

With drain plugs out, reach into carb with deep socket & check tightness of main jets. This also checks the jet holder. If these come loose you'll get this symptom.

Another oddity that will get you is if needle clip was not properly in its seat in slide. It can be fine for some time, then start winding up the return spring in slide.

Also make sure chokes don't vibrate on from loose lever screw.

We ride bikes in <95 all summer long. They don't do that. Worn slides don't do that. They die at idle or a trace above idle. The fat o-rings work good. I'm in same situation with city riding to reach fun roads. I can assure you the carbs will feel warm to hot in stop/go traffic. The air flow through carb at idle is not enough to keep it cool in that kind of heat. Just the hot air coming from surrounding cars is staggering, then add your motor heat.

I always set air gap to .045". Stack feeler gauges as needed to measure. Spec is .040-.060". I find .045 gives more pressure to ring so carb isn't as wobbly. Also if you have choke bracket on left intake manifold, make sure bolt is tight & no air leaks at hole. Also wiggle manifolds & make sure the carb studs haven't backed out allowing manifold to get loose at head. I will restate, phenolic spacers will give no advantage in keeping carb cool compared to thick 70-9711 ring. Also make sure you have cup washers & the rubber ring under cup washers & lock nuts.

Something is wrong, it's not vapor lock. While you could get vapor lock, it would not cause the symptom you state at 1/3 throttle. I've never seen that on my bike or any others & I ride with lots of people. In the city it can be 110f+ . We'll ride for an hour stop/go. The heat off motor is staggering. The gas tank is hot to the touch as is the gas inside. They still don't do what you describe

When fuel gets too hot in bowl, you'll have to hold throttle on. Blipping is more accurate. Still once under way it's fine.

What ignition system are you using? What grade fuel are you using? Always use highest octane available. Out here I find Shell gives best hot performance. Chevron is good too. Both these have good additive packages. The adds on pump are not hype. They actually do keep inside of combustion chamber, & valves cleaner. We found this at work all the time. Costco & Safeway are to be avoided when possible. Ethanol 10% fuel is sold most places (required in CA). It works good, but best if jets are about 5% larger.

When bike is acting up, what is battery voltage 3000 with lights on? Take volt meter on road test. Pop up seat & check. Alligator clips are really handy on leads.

Also what is voltage to ignition system (depending what you have) where you'll measure. Also make sure ground bolt to front rocker box red wires is tight.

If your bike used to run good last summer in the heat with the same carbs & jets, you know the jets are correct size. If you changed carbs, jets or something that's different.

So you're 15 miles from home. Through town & into country. You ride in country without stopping 10 minutes. Is bike perfect then or still act up? An overheated carb with correct air gap, will cool down in less than 3 minutes. Even 30 seconds of easy power riding at 30 mph will cool the carb substantially.

Do some tests & get back to us.
Don
 

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Discussion Starter #13
Thanks for the super insightful response Don. I won't be able to take the bike out for the additional road/voltage testing you proposed till this weekend, but did want to get back to your (and DTE's) other questions since I was able to check those in a few minutes today. In no particular order:

1. Gas cap vent flowing well.
2. Fuel flow from petcocks to drain plug looks strong. I replaced the petcocks this past winter so am not concerned about those.
3. The main jets were tight.
4. Manifolds weren't loose. The choke bracket bolt was in place and tight (no chokes on carbs).There is 0.06" of clearance between flange on carbs and manifold, so on the wider side of spec.
5. The needle clip was in place on both needles, and not being held up by the spring. I did notice that one of the slides was saturated with gas. Not sure if this is a symptom, or perhaps I inadvertently did this when checking flow from fuel tank out of the carb bowl drain plugs (could gas creep up the the slide this way?).
6. I use good quality fuel. Premium Shell gas only. I always add SeaFoam as well.
7. It is a Boyer ignition system.

Neal.
 

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Hi Neal,
The fault consistently developed starting around 1/3 throttle opening regardless of engine speed.
How old are the needles and, more particularly, the needle jets? The latter are brass so not only do the harder steel needles wear them, corrosion also wears any jet - the enlargement can be invisible to the naked eye but nevertheless equivalent to a larger jet orifice.

The fault developed sooner than previous times, about 5 minutes into ride.
Towards the end of the ride, the bike was running really rough, and it wanted to quit at stop lights.
When I got home and let off throttle, bike sputtered and died.
Boyer ignition system.
Notwithstanding the "Healy Diagnosis", I'd make some electrical checks:-

The "Boyer" has either a Black "Transistor Box" labelled "MicroMarkIII" or "IV"? or a Red "Transistor Box" labelled "MicroDigital"? If so, the coils are '6V'? If so:-

. The resistance between particularly the stud terminals of each coil is between 1.5 and 2 Ohms? Repeat the test between corresponding spade terminals, any increase in resistance indicates corrosion between spade and stud.

. Resistance between a coil's HT terminal and LT terminals should be 5,000~7,000 Ohms, the lower the better.

. Resistance between any coil terminal and the case should be tens of thousands of Ohms - some meters display the infinity symbol - looks like an "8" on its side.

. If the above checks appear correct when the coils and engine are cold, be prepared to repeat them on the road when the fault occurs, the fault might be when a component is warm.

The "Transistor Box" Red wire is connected directly to the battery +ve terminal itself (not to a coil terminal as shown in either B-B fitting instructions wiring diagrams)?

Similarly, the coil wire shown as "Red" in both the MicroMark and MicroDigital wiring diagrams is connected either directly to the battery +ve terminal itself or at least into the existing harness Red wires at a snap connector, not to the "Positive Frame Earth"?

You can see a harness Red wire attached to an engine component?

Prepare a 'bypass wire' long enough to connect the Transistor Box White wire directly to the battery -ve terminal. Include a blade fuse holder, make this wire long enough and position the fuse holder where it'll be accessible when you're sitting on the seat; reason is when you connect the wire to the Transistor Box, you're bypassing both ignition and kill switches, the only way of stopping the engine is pulling the fuse. Carry the (7.5A?) blade fuse in your pocket but also insulate the terminal that'd connect the bypass wire to the Transistor Box White wire.

The idea is you start off with the Transistor Box White wire connected as normal to the harness White/Yellow wire from the kill switch. If/when the misfire starts, stop, disconnect the TB White wire from the harness White/Yellow wire, connect the TB White wire to the wire connected directly to battery -ve, insulate the harness White/Yellow wire terminal, fit the blade fuse in the bypass wire and see if the bike will work normally. If it does, the problem causing the misfire is somewhere between battery -ve and the harness White/Yellow wire - possibly fuse, its connections, ignition switch or kill switch, or a combination ...

Hth.

Regards,
 

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Hi Neal, Did a 65 mile ride today. Normal road closed for repairs, so took freeway. So unable to evaluate heat of carb before 19 miles. Then no city riding. However on way home I took normal route. Rode 30 miles on highway, then 3 miles of city. But not stop/go with short blocks. Pulled over & felt my carb. 95f degree ambient. Shell E10 91 fuel our best.

Bowl was very warm to touch, but I could hold finger on it indefinitely. The stud nuts smoking hot, can't even start to touch them. Front carb flange near nuts too hot to hold finger on. Front flange at top center very hot. Could hold finger on it for maybe 5 seconds at longest. Where the casting on top flange has rib up to the slide area I could hold finger only a few seconds. The main side area very warm to touch, but I could hold finger indefinitely. But just barely. Carb top same hotness. I wonder if a lot of this heat is just heat blown back off motor fins.

Side of carb & the round area float bowl seals to quite warm, but not hot. Hotter than side of bowl for sure.

Air inlet where air filter attaches was just good & warm. Decidedly the coolest part of carb.

Bike idled, ran, accelerated perfectly in every way.

I can for certain on smoking hot day 100f+ in about 8-15 blocks of stop lights every block the slide area is too hot to touch with bare finger. Shutting off motor 10 minutes, then tickling before hot start, impossible to even tickle with bare finger tickler is so hot.

I felt John's carbs on '69 Bonnie to compare. He has thick phenolic insulators. Exactly the same. He brazed special made longer studs to use these insulators. He wanted cooler. They made no difference.

So I don't think carbs are root problem at this point.

Stuart gives a really good check list above. Thing is when bike is running good it will usually test good. So you need to ride it until it acts up. Only then test. If possible, you can return home to test, or take tools & jumper wire etc on road test & test on side of road in safe place.

You may want to practice the above tests at home so you'll know exactly what to do if you need to test on side of road. I've done this road side testing on a few occasions. A pain, but it really pays off.
Don
 

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Discussion Starter #16 (Edited)
Thanks Don and Stuart.

I am leaning towards an electrical fault after reading your comments and thinking about this a little more. If one cylinder was at fault, I would think carbs, but since both cylinders are at fault, just seems more like an electrical issue that has crept up on me.

Stuart, to answer your questions...

How old are the needles and, more particularly, the needle jets? The latter are brass so not only do the harder steel needles wear them, corrosion also wears any jet - the enlargement can be invisible to the naked eye but nevertheless equivalent to a larger jet orifice.
No idea. Could be original to the bike as far as I know. It was low mileage when I bought it. If jet was worn, I would expect a slightly rich condition, no? With deposits on spark plug? I don't see that.

The "Boyer" has either a Black "Transistor Box" labelled "MicroMarkIII" or "IV"? or a Red "Transistor Box" labelled "MicroDigital"? If so, the coils are '6V'? If so:-
MicroMark III. 6V PVL coils.

. The resistance between particularly the stud terminals of each coil is between 1.5 and 2 Ohms? Repeat the test between corresponding spade terminals, any increase in resistance indicates corrosion between spade and stud.
2.3 ohms, for each.

. Resistance between a coil's HT terminal and LT terminals should be 5,000~7,000 Ohms, the lower the better.
Right around 6k ohms, for each.

. Resistance between any coil terminal and the case should be tens of thousands of Ohms - some meters display the infinity symbol - looks like an "8" on its side.
Infinity, for each.

. If the above checks appear correct when the coils and engine are cold, be prepared to repeat them on the road when the fault occurs, the fault might be when a component is warm.
Will do....but first I have noticed some inconsistencies in wiring. Note that these inconsistencies have been present ever since I have owned the bike, and it has run fine up until this point. Nevertheless....read on...

The "Transistor Box" Red wire is connected directly to the battery +ve terminal itself (not to a coil terminal as shown in either B-B fitting instructions wiring diagrams)?
Connected to a 2-stud coil terminal, the other stud goes to the '+' terminal.

Similarly, the coil wire shown as "Red" in both the MicroMark and MicroDigital wiring diagrams is connected either directly to the battery +ve terminal itself or at least into the existing harness Red wires at a snap connector, not to the "Positive Frame Earth"?
The transistor box Red is connected to the coil terminal '+' on coil #1. The '-' on coil #1 is connected to the '+' on coil #2. The '-' on coil #2 is connected to the transistor box Black.

The transistor box White wire is connected to '+' on my bike. But the wiring schematic indicates this should go to '-'. Which is correct?

You can see a harness Red wire attached to an engine component?
Yes, on top of the front rocker box cover.

If the Boyer is, in fact, wired correctly, then I will try the test when the fault develops and the bike is good and warm.

Neal.
 

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Hi Neal,
How old are the needles and
needle jets?
No idea. Could be original to the bike as far as I know. It was low mileage when I bought it. If jet was worn, I would expect a slightly rich condition, no? With deposits on spark plug? I don't see that.
There's a long-time US dealer who wears a T-shirt printed, "It's The Needle Jet, Stupid". :)

The needle and jet cover 1/4- to 3/4-throttle. You posted your bike's experiencing problems 1/2-throttle and above. Ime, it'd be difficult to be certain one way or the other that any "slightly rich condition" and/or "deposits on spark plug" was or wasn't (a) worn needle(s)/jet(s), because of the part-throttle opening.

Bear in mind, the 'problem' you're experiencing, the cause might not be a single problem in one component but a combination of small problems in several components. Like many of the changes I've suggested, given you don't know how old the jets and needles are (or even whether they're genuine Amal?), two known-genuine Amal needle jets (if not needles too) are cheap insurance?

The resistance between particularly the stud terminals of each coil is between 1.5 and 2 Ohms?
2.3 ohms, for each.
(y) Apologies for lack of clarity here; PVL coils - particularly older ones - have a slightly higher primary resistance than others.

MicroMark III.
The transistor box White wire is connected to '+' on my bike.
the wiring schematic indicates this should go to '-'.
"transistor box White wire is connected to '+' on my bike" doesn't make any sense. Unfortunately, it could mean a DPO tried to convert your bike to 'negative ground' and screwed up. :(

Please clarify:-

The transistor box Red is connected to the coil terminal '+' on coil #1. The '-' on coil #1 is connected to the '+' on coil #2. The '-' on coil #2 is connected to the transistor box Black.
. The "coil #1" and "coil #2" references are can be misinterpreted, thanks to Bransden's shonky MicroMarkIII/IV fitting instructions. :mad: Just so I'm certain, please would you click on the link, have a look at the instructions and confirm you're referring to the coil numbers as shown in the "FIG.1." wiring schematic?

. If you compare Bransden's fitting instructions' "POSITIVE EARTH CIRCUIT" ("FIG.3.") and "NEGATIVE EARTH CIRCUIT" ("FIG.4."), you'll see your description, "The transistor box Red is connected to the coil terminal '+' on coil #1. The '-' on coil #1 is connected to the '+' on coil #2. The '-' on coil #2 is connected to the transistor box Black" is common to both.

. Note Transistor Box White is always connected to battery -ve and TB Red is always connected to battery +ve; the only differences are which wire is connected directly to the battery terminal and which wire is connected through the bike's switches.

. The Bransden wiring schematics (FIG.1.,FIG.3. and FIG.4). all show the Transistor Box Red wire attached to a coil "+" terminal. The schematics also show a second wire attached to the same coil terminal, that goes either to "POSITIVE FRAME EARTH" (FIG.1. and FIG.3.) or to the switch (FIG.4). On your bike, that second wire from that coil "+" terminal, what's the other end connected to?

Hth.

Regards,
 

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Discussion Starter #18
Hi Stuart,

I have some more details for you.

First, I have no problem servicing the carbs to replace old bits. I have been wanting to put a stay up float in there for a while. In fact, this may give me an excuse to finally upgrade to premiers rather than pouring more money into the old carbs, but that aside, I can certainly replace the needle jets and needles.

To the questions about the wiring here's what I can confirm based on the schematics in the Boyer documentation:

1. The coils are indeed wired as depicted in Figure #1. Coil #2 to black on transistor box. Coil #1 to red on transistor box. There is one exception. The schematic shows the '+' on coil #1 to ground through the frame. Mine is wired directly to the '+' terminal on the battery.

2. It is also wired as indicated in Figure #3 (not Figure #4). However, the suspect white wire from the transistor box is giving me a headache. The schematic indicates it must go to '-'. When the ignition switch is off on my bike, this connection goes to '+'. Yet when I turn the ignition on, the polarity reverses and this connection reads '-' as it should. Maybe I am not understanding something about how the wiring on the bike works, but this is quite confusing. The connection point for the transistor box white wire into the wiring harness is at a 3-pronged female blade connection: the white blade connection from the transistor box goes to a white wire female blade connection (the other two female connectors are black/white wires that are unconnected). Have no idea if this is part of the original wiring harness, or some aftermarket kit. But since the white does ultimately receive '-' voltage when the ignition is turned on, I suspect that is why it functions. Is the '+' voltage when the bike is off causing issue?

Neal.
 

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Hi Neal,

Thanks for all the clarifications.

coils are indeed wired as depicted in Figure #1.
wired as indicated in Figure #3 (not Figure #4).
one exception. The schematic shows the '+' on coil #1 to ground through the frame. Mine is wired directly to the '+' terminal on the battery.
(y) Direct to battery +ve is better.

suspect white wire from the transistor box is giving me a headache. The schematic indicates it must go to '-'. When the ignition switch is off on my bike, this connection goes to '+'. Yet when I turn the ignition on, the polarity reverses and this connection reads '-' as it should.
Mmmm ... "polarity reverses" is unlikely. More simply, any break in any circuit - e.g. ignition switch off - any Voltage measurements don't mean anything. That it "reads '-' as it should" when the ignition switch is turned on suggests everything is basically correct.

The quickest and simplest check is with a Volt- or multi-meter set to Volts:-

1. connect the meter just across the battery, note the meter reading;

2. move the meter lead on battery -ve to the connection between the Transistor Box White wire and the harness wire; with the ignition switch turned 'on', the meter reading should be the same as at 1.

However:-
The connection point for the transistor box white wire into the wiring harness is at a 3-pronged female blade connection: the white blade connection from the transistor box goes to a white wire female blade connection (the other two female connectors are black/white wires that are unconnected).
... is odd and would bear further investigation ...

The Transistor Box White wire connected to a harness White wire will work but, unless a PO has done something else, on your bike, TB White should be connected to the White/Yellow wire from the handlebar kill switch.

Digressing hopefully without confusing:-

. Lucas used White as the code for 'switched power' - White wires are energised only when the ignition switch is on.

. White/Yellow was introduced from '71, when new-for-'71 handlebar switch clusters incorporated a kill switch (press-to-break button). Pre-'71, a White wire ran from ignition switch directly to coil "-" terminal(s); '71-on, White goes only to the kill switch, White/Yellow is between the kill switch and, originally, the coil "-" terminal(s).

. When Ernie Bransden marketed his first EI in the early 1970's, he was selling primarily to owners of existing British bikes, the vast majority of which were then pre-'71 so had White wire(s) to the coil(s), So he chose White for the wire into the Transistor Box. However, as time has gone on, more and more '71-on Britbike owners have wanted to fit EI, but Bransden haven't updated either wire colours or instructions. :(

There could be several reasons why, on your bike, the Transistor Box White wire has been connected to a harness White wire, instead of correctly to the White/Yellow from the kill switch:-

. Whoever installed the EI on your bike might've slavishly followed the Bransden fitting instructions without understanding their intent - even on a '71-on Britbike, there is a harness White wire in the vicinity of the coils, to supply the turn signals relay and the rear brake switch.

. There is something wrong with the kill switch on your bike; whoever installed the EI on your bike simply decided to bypass it.

. Whoever installed the EI on your bike also installed a new White wire to the TB White wire from the kill switch (from the end of the White/Yellow wires connection inside the headlamp shell?).

Hopefully for further clarity, your bike being the age it is, the standard ignition circuit negative-side wiring is:-

. battery -ve -> Brown/Blue wire -> fuse -> Brown/Blue wire -> ignition switch -> White wire -> handlebar kill switch -> White/Yellow wire -> (coils);

. as I say, on your bike, the Transistor Box White wire should be connected to one of the harness White/Yellow wires, the end of the other harness White/Yellow wire should be insulated.

3-pronged female blade connection:
(the other two female connectors are black/white wires that are unconnected).
Can't surmise any reason for this:-

. With points, Black/White wires originally connected one coil "+" terminal with its corresponding points and condenser (originally mounted beside the coil on an OIF).

. With EI like the Boyer-Bransden, harness Black/White (and the other original coil-points-condenser Black/Yellow) can be used to connect the Transistor Box Black/White and Black/Yellow wires with the Stator (in the original points compartment in the timing cover) Black/White and Black/Yellow wires.

Hth.

Regards,
 

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Discussion Starter #20
Thank you Stuart. The wiring on the bike has definitely been mucked with. The kill switch was disconnected as was the front brake switch (only the rear brake activates the brake light). There has been a quick connect added for a trickle charger. There are multiple connection points that have been added or spliced in over time.

Is it worth it to try to sort the wiring out (using the original schematic in the workshop manual)? Could a frayed wire or leak to ground manifest as the issues I have been having? Just thinking of the easiest things first before I tackle rewiring parts of it. Probably just to take some readings as you and Don originally advised when the bike starts having issues.
 
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