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Originally Posted by splash
Plugs now look the same after running for a few days after setting timing. Electrode is burnt toast color but arm and circumference where threads begin is black carbon.

Will try cleaning out behind mixture screw as Don explains above.


The electrode colour is good, what grade plug are you using? N3 N4 etc...

With the correct plug you want to see the first 3 threads up the plug showing a discolouration to the metal,


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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I'm glad that Splash has got this problem sorted.

I am going to hijack this thread and say that I tried to get my plugs the same colour as each other but without success. I had my own thread on this once.

Single carb 650 TR6R 1967. I tried doing everything to the points (strobed to perfection). One plug is too light and the other too dark. The dark cylinder does have a bit of oil in it but the plug is dry dark but not fully black or wet looking. I haven't tried a new condenser on the darker side or maybe it is a worn inlet guide on light side? Can this do it? How about a leaking head gasket?

Dave

Last edited by dave jones; 03/24/21 4:32 pm.
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It can be a lot of things.

Two good diagnostic tools are a compression tester which are best done on a warm engine and with the throttle fully open.

The other is a gunson colour tune. This is not only good for setting idle
Mixture but also for diagnosis of oil or over rich contamination.


If you are getting puffs of smoke on over run it’s valve guides. If your getting smoke on acceleration then your possibly looking at rings/cylinders.

If one plug is excessively pale on standard jetting, possibly even that side exhaust pipe looking a bit blue then you could have an air leak where the 1-2 manifold mounts against the head.

If your only using a bit of oil or slightly too rich of mixture then it won’t always be visible in the exhaust smoke but it will show on your plugs. Hence why you should try the colour tune and compression tester.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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Thanks, Allan. Had not seen any smoke. The pipe on the light side is blue but the other side is catching up and looking a bit blue, too. Is an air leak most likely at manifold? The joints look solid. Can air actually pass down the inlet guides?

Dave

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Hi Dave,

An air leak can occur anywhere, but with it being a single carb machine and with your plug diagnosis it limits its possibilities, or at least i think so....

In my opinion, if you have the leak at the carb mount then you would be more likely to see the plugs ceramic white on both pots, you could have a leak at the exhaust, which would draw in air, youd find some back fire and most likely an increase in blue in the pipe. Points ignition can have an effect also as cylinders will be timed differently, if one side is more retarded then the other then it will run hotter...

so a leak at the point i mentioned is the only thing I can think of, unless as I say your using points ignition and there was some failing in that. Electronic would fire both sides at the same time and at 360 crank degrees apart respectively so that wouldn't throw it out. If the condensers or the coils were crapping out, even just one of them, you'd know by how it rides, it would pull fine until you placed a higher demand on the engine (so more speed or climbing a hill) then it would pop and fart and youd have little power at all.

You could compare the primary and secondary resistance across the two coils and check they are somewhat the same. primary resistance should be 4 ohms, I cannot remember what secondary should be.

I doubt youd get any air pulling down the guides, youd get the oil symptoms firstly as previously described.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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Thanks again, Allan.

The bike has always run surprisingly well considering it is not tip top, wear wise. Starts first kick even after a long lay off. Does require choke to start and for a short distance on the road. I thought maybe it was too weak but tried using the choke when fully warmed up on the road but this didn't improve running.

As I said i have noticed more blueing on both sides recently and looking back this may have started when I changed the timing from 36 to 38 before tdc. This seemed to make it more powerful (might be my imagination) but could well be making it run hotter. I retarded the timing because I thought it would be better with modern petrol but I only have low comp pistons.

Could just be running hotter both sides but burning a bit of oil on left but not enough to cause a wet plug. I had the carb bored and the slide sleeved so can't try a different slide (no 4). Could file a bit off but then I would be stuck.

The carb sleeving didn't make any difference to road running but made it so that it idles properly. Previously you had to set it for one or the other. If set for a regular idle it would eight stroke around town. When it was set for the road it would idle but would gradually peter out. I don't understand this. You would think it would idle or not idle! Now you can set it for a regular idle and it still runs smoothly around town.

Did get some help on needle positions from Nick Smith. I thought mine was on 1 he said it should be 2 and turned out that it actually is on 2!

Dave

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This is absolutely normal. Not having to use the choke is what is abnormal.

Quote
Now you can set it for a regular idle and it still runs smoothly around town.

What are you setting: Pilot air screw or idle screw?

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If it’s 8 stroking around town then your slide is probably too rich. You also need a certain amount of clearance around the slide, too much abs you loose the vacuum applied against the jet and pull less fuel through and too tight and you pull more fuel through. As long as it works smoothly and freely then jet the bike from there.

You spend a surprisingly large amount of time riding on the slide setting. But the other thing to note is the needle jet and needle wear. I like to replace these as a set. As these wear your making the flow past the needle jet greater, this will cause your 8-stroking. Change these and go for your run, try some rural routes where you can get your speed up but also be slowing down for bends etc, this will give you a good idea of if you need to go leaner or richer. At this you won’t spend much time on slide position. Mark the throttle at closed, fully open, half way then 1/4 and 3/4 positions and then mark the body so you know which throttle position your riding at (I tend to use some Insulating tape)

Once your happy with your needle position and the bike is pulling cleanly as you decelerate and accelerate through bends and adjusted to suit.

Top slot on the needle is pos 1, bottom is pos 3, pos 1 is a leaner setting.

Now, with the engine nice and hot, put it on its stand and adjust the idle
mixture, screw the horizontal screw out as far as you can before the revs start to drop, then steadily screw it back in, the revs will rise then start to drop again. Find the sweet spot here and leave it. It could be revving at 2000, don’t worry at this point. Adjust the idle speed by screwing out the diagonal screw until your at about 1000 rpm. Now check the horizontal screw again, and again find that sweet spot. Depending on how far out the throttle slide was, depends on how far out if any the mixture (horizontal) screw is)

Then go on a town run, where your stop-go through traffic. You’ll find out soon enough if your running rich or lean. 1 slide too lean is usually the slide where the engine wants to hesitate or stall when pulling away. If you have to feather the throttle, go one slide richer.
If the bike pulls but it’s a bit sluggish, go one slide leaner.

The lower the slide number the richer it is, the higher the number the leaner it is. With a standard exhaust your usually somewhere between a 3 and a 3.5 slide. But how the bike responds best is the right setting.

Also going to a bigger number 38 degrees from 36 is advancing the ignition This will give you a steadier tick over and better acceleration. You might find a slight drop in power at top speed however. But this is compared against the optimum setting.... this you need to find out yourself.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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1/8sHi splash, Mark grip with masking tape in 1/8s. Take cable slack up for zero. Be accurate. Mark zero & full. Then divide by halves until you have 1/8s.

Print this tuning guide & take in pocket on road tests.

https://static1.squarespace.com/sta...2/1481956877861/Amal+MK2+Carb+Manual.pdf

Make sure you have stay up float & aluminum tip viton needle. Set float level.

Make sure you have PERFECT needle jet & needle. Any wear will skew results & you'll never get carb to work. If in doubt get both new. Get only genuine AMAL parts.

'70 Tiger is one of the best bikes Triumph ever made. They can be made run perfectly. One of the best running of all. If not, it's not right.

It takes time & practice to tune carbs. Several road tests & comparing tuning guide. Always keep throttle opening in mind. This tells you what part of carb is controlling mixture. The tuning guide will show you what to do to change mixture.

Want to mess yourself up? Don't mark grip, don't set float level, don't get perfect needle jet & needle. Don't print, study & take tuning guide on road test.

Tip, main jet can be hard. Find a moderate up hill. 65 mph or so full throttle. Go larger main jet until 8 stroking. Misfire that goes ah ah ah ah, back off throttle it stops instantly. Wide open, comes right back. Go one main jet size smaller at a time until 8 stroking stops at full throttle. Find a road test route that works for you. Keep same route so you can get repeatable results & feel what changes does what. I like to start with main jet if bike runs good enough to allow it to run 65 mph.

So what does the snap throttle do? That is very strong indication of cutaway.

With motor heat soaked pull over & let idle. Turn throttle slow as possible. If motor dies or wants to die just off idle, it usually indicates carb is worn out. I fyou cheat mixture lean 1/4-1/2 turn out from best idle with mixture screw, the slow throttle is better, that confirms wear slide/bore. Don't jump to conclusions. Get repeatable results over several road tests.
Don


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And what do you gain by marking 1/8ths? Or 16ths for that matter? If you mark in 1/4 you have 5 marks which hit the same 5 points as indicated by the tuning guide which you kindly linked to.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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Thanks Allan and Don.

Don is mixing me up with Splash. I shouldn't have hijacked this thread.

John Healy. With the sleeved carb the idle is set a bit richer than 1 1/2 turns for good running.

The point I was making was that even though the bike is a smooth runner through the range it still has plugs of different colours.

I had better leave this thread now


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Quote
I fyou cheat mixture lean 1/4-1/2 turn out from best idle with mixture screw, the slow throttle is better, that confirms wear slide/bore.

If you have a "worn out" carburetor it usually refers to the slide bore is worn oversize. Most the wear typically appears at the bottom edge of the slide and adjacent area in the body. This lets more air enter the intake manifold reducing the vacuum signal on the fuel metering systems. The most affected period is at very low throttle openings.

Turning the air mixture screw out 1/4 to 1/2 turn further reduces the vacuum. It is as if the body was worn more. Turning the air mixture screw in a 1/4 to 1/2 turn increases the vacuum signal. This compensates for the lack of the vacuum lost by the worn slide/body.

Years ago AMAL increased the clearance on the slide for safety reasons. It help prevent the slide from sticking when the mounting hardware is over tightened. To do this they had to make changes to compensate for the loss in the vacuum signal. They did this by making changes to the body and the related bits.

If this clearance isn't maintained when sleeving the carb it throws all of the low throttle opening jetting askew. To get the low speed jetting to work as designed you are looking for around .0035" clearance. If less, corrections have to be made and you have to be very careful when tightening the mounting hardware.

For design/engineering reasons, if you choose to use a Stay-up float, you should always use it with an aluminum needle. Otherwise the old white float and brass needle still work as designed.

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To the point of different spark plug readings: The differences can be down to the difference in air flow (velocity) from the draw of air created by each cylinder. The air velocity is dependent upon a handfull of conditions that are independant of the carburetor. You must consider the condition of the pistons rings, valve seating, cam overlap, ignition and a handfull of other factors.

If the vacuum signal of each cylinder provided by the downward movement of the piston, is not the same, neither will the amount of fuel delivered be the same.

While the effect will be slightly different for a TR6, with its single carburetor, as it is for a T120 you can see differnce. A good place to start looking into this, as a factor, is a compresion test. Without a large air plenum to balance off the vacuum among cylinders, if the air velocity from one cylinder is less than an other, the amount of fuel delivered to each cylinder can vary. It isn't always the carburetor.

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Some individual models of the BSA pre unit twins exhibited what is known as "induction bias".
For reasons related to what John H has has described together with tolerances etc with a single carb each cylinder did not get the same as the other in terms of cylinder filling etc.
It was so much of a problem that BSA made available a tapered gasket to go between the head and the carb to direct the incoming charge towards the weak side.
Might be worth trying it on your TR6.
HTH

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I can tell you for sure that mixture bias happens on single carb Triumph twins too.

I don’t know if slanted spacers fix it, but I know that twin carburettors can fix it.


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TM and TT, any thoughts as to the cause?
Is it always to the same side, or does it vary? That would be an important clue.

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Originally Posted by koan58
TM and TT, any thoughts as to the cause?
Is it always to the same side, or does it vary? That would be an important clue.

Fluid dynamics ain’t so simple as putting a Y-piece in front of a carb and assuming everything will be fine.

The left one was weak on my bike.


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"Fluid dynamics ain’t so simple as putting a Y-piece in front of a carb and assuming everything will be fine."

Why isn't it? Fluid dynamics has no left/right preference.

If the only example you've experienced is your own bike, I'd be tempted to explore the other factors JohnH mentioned in his second post.
Or even the precise profile/position of the "parting of the ways" inside the manifold.

I'll be waiting for someone to bring Coriolis into it!

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Koan-- IMHO the important factors are wear and tolerances.
JH has IMHO correctly pointed out how wear--differential between cylinders can affect how one cylinder performs compared with its supposed twin.
Tolerancing on the Y manifold, how the Y manifold sits on the head studs, the position of the head studs---just to give some examples---can affect one cylinder relative to the other.
In the case of the BSA pre unit twins I believe that induction bias was found more on the 500cc A7 than on the 650cc A10---but don't ask me why!
The concept of the tapered gasket is to "direct" the gas/air mixture from the carb towards the cylinder running the weaker.
Note that I am not suggesting that induction bias IS the cause of Dave's problem--it is just one of the various possibilities.

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Dave You see, it is Rocket Science beerchug

It also could be what you are seeing is the difference in how well the rings are at oil control. It goes on and on. Where is Dr. Rob Tuluie when you need him.

Unless the problem is keeping you from riding I would go riding.

Coriolis: I thought that they were a Mafia family.

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“Dave You see, it is Rocket Science”

John, it isn’t obvious which Dave you were talking too, but as at the end you mentioned “Coriolis” I guess it was myself.
BTW I only mentioned that word jestingly, it is the phenomenon that is supposed to determine whether bathwater spirals down the plug-hole clock or anti-clockwise, depending on whether the bath is in the north or south hemisphere.
In truth, what happens at the plug-hole is determined by local differences such as waste pipe verticality, exact shape and lateral levelling of the bath blah. Which is what I suspect this “intake bias” amounts to.

I appreciated your “Rocket Science” until TM took the wind out of it by saying it was the BSA 500’s(A7) not the spaceage 650’s.

Some things mentioned by TM seem quite possible, in particular the fit (with possible steps) between manifold and head. Also excess gasket could be an issue here too.

It seems that Splash is happy with his plug readings having now got his ignition timing correct, and we are subsequently discussing dave jones plug readings (which are different between shades of tan but the bike works fine).
I think that is the realistic objective, not to aim for identical depths of colour, but beware of white insulator and top arm burnt white for much of its length. Carbon on the end of the threaded end doesn’t concern me at all.

Only my thoughts, Corleone may have had a different view, but perhaps on vespas rather than britbikes!

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These plugs are from my T140 after a 12 mile run in high gear between 55-75 mph on a backroad in a a sporty manner but not wide open throttle. The plug shows slightly rich combustion and a slight difference in color. Fuel is 90 octane non ethanol..

5jEkJaX.jpg

79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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A pic can be misleading, but they look white and hot to me, especially the left one.

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I was thinking the same thing. But who knows what is right for a certain bike? The plugs and valves on my 56 T110 were snow white and it was a rocket. But that was (oh my God) 58 years ago.

Last edited by desco; 03/27/21 2:39 am. Reason: change

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How about this one, same bike but a harder run and cleaner shut off than above....Surprized you missed the clipped electrode NGK Competition plugs...The engine has Mikuni flatslides.

76vqPIH.jpg

79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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