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#740851 07/05/18 5:39 pm
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I don't know how many times I've sworn at the lack of clearance for the throttle cables on a Triumph Bonneville. No matter how you route them, they'll enter the carbs at a very flat angle, making them stiff to operate and prone to wear and coming out of sync. Why didn't they make ample cut-outs under the tank to simply make it a non-issue? frown

I've used Venhill cables as they're a bit more pliable but on my 66 and their Monoblocs I'm stuck with Doherty as Venhill don't make cables for these. Anyway, they don't rally solve the problem as such either.
Extra rubber under the tank mounts helps a little too, but not enough. On the OIFs you can simply substitute the mounting stud for a longer one and use as much rubber as you need, so it's less of a problem. On the earlier T120 you're pretty limited unless you manufacture a set of longer studs, which is what I intend to do, and use double rubbers.

There will be people on here that have found a solution. How do you guys/gals cope with this? help

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If you can find them, get the braided cables. They're much more flexible than anything out there. Also, I shape the cables where they enter the carb, by carefully bending he cable outer until it holds a curve.

Cheers,
Bill


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Thanks Bill,

Not much in the way of choice around here. What did you have in mind? If not available here or in the UK, I have friends in high places in the US. One actually.
If he survived 4th of July (redcoat...). Take a bow Richard.

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I remove the cable adjuster from the top of the carb, discard the adjuster, drill the hole just big enough for the cable to fit in, its not much but helps a bit

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Yup but that's standard Triumph, so it's what I have. The adjusters are on the cable, rubbing on the tank. sick

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Perhaps something like this at the carb cap would help, though it will probably require reworking the cable. part# 97-0670
[Linked Image]

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Thanks for the intro, Stein Roger!
Yes——survived 4th July OK— I call it Terrorist Day and hoist the Union Flag!
The curved cable guide may be worth a try–but you certainly don’t want sticking throttle cables—-that gives real brown pants moments!

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Originally Posted by Tridentman

Yes——survived 4th July OK— I call it Terrorist Day and hoist the Union Flag!!



Sorry, Richard, couldn't resist! laughing

Cheers,

Steve

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Fitting round pegs into square holes since 1961...
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He he... nice... laughing

Back on subject, in actual fact there isn't much room for the bend either, but I'd be prepared to try. Which means I'd have to make my own cables, or perhaps modify a set of Venhills. I like those, and have never had one snap on me, unlike their clutch cables in certain applications.

One idea I've had, but haven't been able to sort out, was to apply some kind of bend on the outside of the cable.
I tried shrink wrap but it had too much springiness in it and wouldn't stay curved. I've thought about wrapping wire around it, but haven't tried it out yet.
Suggestions more than welcome!

Modifying the tank with cut outs would be nice of course, but that's NOT going to happen any time soon...

I had a set of nice braided cables on a US import Bonnie a while ago, very pliable and with a sweet action, but I couldn't find out what make they were.
The Doherty brand cables are stiff and seems cheaply made, though they're certainly pricey enough to buy!

To sum up the ideas so far:

Raise the tank.
Braided cables.
Install a bend in or on the cable.

More ideas? Anyone?




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three options, use mountain bike rear brake noodles for the swept bend to the carb ( I use this)

proper swept bend as mentioned above,

plastic reinforcing sleeves, they help a bit but tend to come off.
i get the noodles from my local push bike shop and make up cables with them, gives a very light throttle and makes most use of limited space.
https://www.amazon.co.uk/RICISUNG-Brake-Noodles-Mountain-Bicycle/dp/B07D7VHC1B
the top hat end goes to the carb lid, in line adjusters up near the bars for ease of access.


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Thanks Gavin, now that sounds like a good idea. You use two cables then, like on the same year Triumphs? Mine has the splitter box, and I considered converting to twin cables, but it's a very original bike so I decided against it.
I lifted the tank at the rear with a longer bolt and two rubber donuts on top of each other. At the front I used a little less, but it did work quite well so I'll leave it for now.
Sadly, I'll need to sell the bike, partly to finance my next Bonnie project, on which I'll look into using those noodle thingies.

Sorry for the delayed response, been out motorcycling with friends, all on Triumphs. Brilliant weekend crowned with a festival and Jeff Beck last night.
Magic! I still can't believe I was but a few meters from the legend.

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Gavin, reviving an old thread here but did you need to "fettle" the "noodles" beerchug. wink

I ordered a few and my bend is much too large to let the tank drop as low as it must be to be attached correctly. One can see the large gap between tank flange and frame boss on the right of photo

[Linked Image]

Last edited by BrettF; 11/22/18 5:26 pm.

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I think this is a great idea of Gavin's. Of course they are designed for their bicycle application, hence the large radius, which doesn't suit yours.

Tubing can be bent to much smaller radii, a rule of thumb is a minimum radius of 3X the OD of the tube. Very roughly, from your picture, the radius is about 10X tube ID. (so say for instance, the tube is 5mm, then the rise is 50mm).

I'm only throwing thoughts out now, it looks like it may be possible to disassemble the 3 parts of the noodle. If so, you may be able to get a brake pipe maker to bend it further, or supply a pre-bent corner of the same OD. Then trim the carb end to the minimum straight length to fit the socket.
With a small enough radius (say half the present) that you don't need to go the full 90deg, and can have the cable entering in its natural downward way.

The principal "unpleasantness" of having that nasty angled entry of the cable into the carb top is that the cable inner is bent through an angle over a sharp edge (the end edge of the outer coil). In addition to the severe bending stresses, a high pressure is exerted on the small area of contact. Bowden cable no-nos.
To try to persuade the cable outer at this point into a permanent bend is unlikely to be a long term solution, though may not be any worse than the original problem, particularly with single carb. No good with twin carbs.
The moment you've bent the outer spring beyond its elastic limit, it has been compromised. It can no longer to be relied upon to return to where it started. If you have 2 of these bent cable ends, at which level of throttle tension can you be confident for synching?

Having said all that claptrap, the reason that the cable end can be at such an angle in the first place is that the ferrule so slack within the receptacle, and the receptacle within the carb top, allowing it to lean as it does.

My machine is different to yours, but this concerned me decades ago. I have used the threaded adjusters in the carb tops for a long time, not just for their convenience (I still have cable adjusters under the tank which are used for initial setting) but the cable ends are a much more positive fit into them such that they can't exit in the way we're concerned with. Minor synching adjustments are also easy.

How much distance do you actually have from the carb tops to where the cables approach? I wish I'd asked that first!

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Yup , they are easy to bend, I tweak mine slighltly, opening them up just a bit. They have been on for 10 K with no issues, usually by now the outers backs would be broken, carb adjustment has stayed stable when set ( apart from changing slides). I suppose eventually the steel inners will saw through the nylon sleeve, but so far so good.
My throttle cables are two into two, no splitter box. Choke cables have a splitter

i see your clearance issue, my noodles swerve inwards and sit between the tank cheeks in the tunnel,, the bread bin tank has cutouts here for a bit more clearance. I only used them for the throttles , the choke cables I used a split plastic sleeve from Venhills, it was too tight for the noodles.

I also see the gap, is there not some sort of rubber mount bit fills most of that?

Last edited by gavin eisler; 11/22/18 11:12 pm.

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I fiddled a bit last night and managed to tighten the bend on one side and open the bend on the other to get something that should fit. Would have been much easier with a longer tube to start with - next thing to look for ;-)

Gavin, you are correct, there is a rubber spacer between the tank and the frame but it is at max about 10 mm, while in the photo there is about 25 mm of space with the "large bend noodle".

The noodles I received had 50 mm from carb top to the top tangent (bottom of the tank), as per the photo. I massaged them to have 35 mm between the carb top and the top of the noodle when installed. Looks like it will work OK. I'll slowly make new lower cables over the winter. I plan to do this for both throttle and choke while I'm in there.

Note, I've a 71 engine in a 67 frame so I don't know if the 35mm-odd space between carb top and tank is normal or not.....

Gavin, what was the dimensions of your noodle? laughing


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Its freezin in the shed and access is tricky to my noodles without gettin the tank off, they look about the same as the ones in the pic, I tweaked up the front part so the cables run parallel to the top tube, with the cable in its fairly safe to nudge them around without collapsing the tube. i grabbed mine from a pile in the LBS, there arefront bends and rear bends, rear bends are more acute, tighter radius, and would need more straightening out. I think I used front bends.
Any decent cycle shop should have stacks to chose from.


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OK for a race maybe, but in road use I can imagine the copper eroding rapidly and splitting in short order. Surely copper is just too soft?
I don't know the relative hardnesses of the inner and outer of a Bowden cable, I suspect the outer is harder, anyone know the facts?

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Originally Posted by gavin eisler
). I suppose eventually the steel inners will saw through the nylon sleeve, but so far so good.


Thanks for mentioning that! I assumed the nylon inner was just to hold the parts together and should be tossed (it was flared to hold the large interface tube in place), but I just tested and standard throttle cable goes through the nylon perfectly.

I've decided to dump the choke, after a season of some coldish riding it has never proven necessary.

Cheers.


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Something I just stumbled upon from Venhill... Wonder if it works?

[Linked Image]


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I use these on the choke cables, better than nothing, they can pop off when you are moving bits , otherwise good.


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Originally Posted by gavin eisler
Its freezin in the shed


Lol, good. You did not have much empathy for me last year when you had me tracing every electrical connection last year in my frezzin cold garage.


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Interesting thread. I have puzzled over this for a long time. The threaded carb tops seemed to at least allow a straight entry and I have some on the shelf.

I was warned that you don't want to capture the cable in a bend. The plastic ones which might flex seem to be a good solution.

Although this might be a solution in search of a problem.


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A Q&D solution if you do have a cable adjuster on top of the carb (or, in the case of Mikunis like mine, a brass spacer), slip a length of 1/4" fuel hose over the cable and over the adjuster or spacer, clamp the hose to the adjuster, and have the hose extend up under the fuel tank. This keeps an even radius on the bend in the cable and keeps it from bending sharply right at the carb or climbing up out of the adjuster.

Someone jokingly asked me once how I was able to feed fuel to the carbs at the top.


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Mikuni make some angled adapters in 45 and 90 degrees. Probably the wrong threads to screw into Amals though. And, you do need to modify the cables.

Mik45.JPG

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I have used these on a pre unit bonnie, l can say that they do work very well.
Ken


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