Jump to content

1969 TR6 PI Choke cable


Recommended Posts

Hi all

I need a cable for my car. After a look around at the usual suspects they are not cheap for what they are. There also seems a number of types in terms of different lengths, construction in terms of solid or flexible core and the pictorial on the knob. So its a bit confusing what to go for.

So before I order can people offer opinion on who makes the best one and is correct for my year of car in terms of the length etc.

As ever thanks for advice.

Andy   

Link to post
Share on other sites

Andy

When I replaced mine a few years back  the info from several suppliers was that they came from one source British Motor Heritage. The first one failed within weeks and was returned ,the second one broke quite recently ,this one I managed to repair at home. 

As for length the longer one fits with less strain at the bends and you have a bit of extra to play with if you need to repair.

Brian

Link to post
Share on other sites

Thanks Brian

Joy as ever poor quality replacement parts. 

I was hoping there would be a choice, from what you are saying get the long one and hope when it fails there is enough length left to affect a repair.

Andy 

Link to post
Share on other sites
On 9/22/2020 at 8:57 AM, brian -r said:

Andy

When I replaced mine a few years back  the info from several suppliers was that they came from one source British Motor Heritage. The first one failed within weeks and was returned ,the second one broke quite recently ,this one I managed to repair at home. 

As for length the longer one fits with less strain at the bends and you have a bit of extra to play with if you need to repair.

Brian

Hi Andy!

They can be repaired by using motor cycle throttle cable kits from Vehicle Wiring Products and use teflon lined outer jacket which gives a much soother operation and you have the choice of length to suit! But you may need access to lathe?

Bruce.

Link to post
Share on other sites

Hi Andy,

I managed to repair mine earlier this year using a bicycle brake cable from Halfords. 

I cut the two cables off of the base of the choke mechanism and then drilled out the solder plug in the side, then drilled down the length of the rod to remove the remaining debris.  All was done with a battery drill just holding the choke knob in a vice.  Just require a bit of eyeballing to keep it straight.

 

I chose to tin the ends of the cable with solder first. (You need to first wash them with methylated spirit and then use flux before soldering) and then inserted them into the cleared hole.

Once they were in place I added a little more solder to the assembly to fill the side hole.

For belt and braces I also squeezed the finished end in the vice to make sure it had griped the cables.  This dents it a bit, so you will need to tidy it with a file to ensure it slides in and out the sleeve properly.

 

So far mine has been good for six months and only cost me about £5.00

 

This is the link that gave me the inspiration to try:

https://www.triumphexp.com/forum/tr6-tech-forum.2/double-choke-cable-repair.1369685/

Best of luck,

 

Tony

Link to post
Share on other sites

Andy, I did the same as Tony, to make life easier remove the grub screw from the knob, this allows the whole thing to be removed from the rear. A couple of photos   

IMG_3971.thumb.jpeg.72639d5b194c841bc6e369ec1a40a53e.jpegIMG_3964.thumb.jpeg.80dee8c557716c11a97139040f320425.jpeg

IMG_3972.jpeg

Link to post
Share on other sites

Thanks all for the DIY options just what I like as a tight Yorkshire type. Obviously we are not alone!

No lathe but I'm sure a mate will help all I need is a broken one to fix as I don't have one to even fix. Anyone got one kicking around?

Again thanks 

Andy

Link to post
Share on other sites

Andy, I didn't have a lathe just a small electric hand drill using a 2mm then a 3mm HSE drill in a bench vice, and of corse a steady hand. Your not drilling steel just the old solder 

Link to post
Share on other sites

Hi,

if buying new there are different length cables depending on whether the car is early or late PI, or carbs. Revington describe the lengths for an early PI like yours as 1230mm/1055mm, whilst SC parts  say 41.75/49.25 inch, which works out fractionally longer. When mine broke I bought one from TRGB who were the only people with stock available at the time. It works ok, but the twist and lock function is not very good, in fact after some use it stopped working but the friction is sufficient to use it as a normal push/pull cable. Also the knob is not detachable.

Mike.

Link to post
Share on other sites

You could consider ignoring the fast idle cable and just running a cable to the metering unit, once the engine has been running a short time the fast idle is redundant. The last new choke cables I bought were very thin compared to the originals and I was not very impressed, I did wonder if an MGB one would be about the right length.

Rob

Link to post
Share on other sites
1 hour ago, Robert Price said:

You could consider ignoring the fast idle cable and just running a cable to the metering unit, once the engine has been running a short time the fast idle is redundant.

That's a good work-around, but it is pretty satisfying to have the engine start from cold and settle into a smooth (ok, rough) idle without any use of the throttle and no long cranking. That needs enrichment and a fast-idle cable. Or, before Tom chimes in, Webers!

John

Link to post
Share on other sites
3 hours ago, JohnC said:

That's a good work-around, but it is pretty satisfying to have the engine start from cold and settle into a smooth (ok, rough) idle without any use of the throttle and no long cranking. That needs enrichment and a fast-idle cable. Or, before Tom chimes in, Webers!

John

John,

I'd agree, get the MU cable pushed in early.

I have an arrangement with a 2 cable set-up, the original Choke cable goes to the MU (one wire only is connected) . The additional (lower) choke knob (mounted lower down on the H frame) goes to the fast idle throttle position. This stays out as long as needed, its only engine revs after all.

Two single cables does the job.

Bob

Choke knobs portrait.jpg

Link to post
Share on other sites

Hi all

Thanks for the feed back. You will have to bear with me as I come from the world of EFI but I'm determined to keep the car on the OEM PI so will have to learn.

Bob If I'm understanding this right on a early PI for a cold start one cable to the metering unit gives enrichment. The other cable goes to the fast idle cam to control the butterflies to increase the revs until warm. So once started in theory you are using increased revs only to prevent stalling using a single cable until warm rather than enrichment on the other separate cable which is pushed in once engine start achieved . A single double knob would provide both even though enrichment is not really required after start. 

Having single cables to both allows better control during warm up. Mechanical EFI!

Did Triumph use one single double cable as a lazy option more appealing to the average driver used to a sgl choke? 

Having less enrichment seems sensible if only to cut down wasting fuel. However if particularly cold you could keep the enrichment out a bit longer.

Gives me another option to consider.

Cheers

Andy 

Link to post
Share on other sites

The enrichment and fast idle cables operate cams, which are shaped to provide the appropriate amount of enrichment for a given fast idle setting. Triumph wasn't lazy, they used mechanical means to achieve what we now use electronics to do. Perhaps not as well, but still pretty effective. The main issue with the cams is that they work to tight tolerances, and wear in the linkage bushes etc makes them hard to set up correctly. Like many things to do with the PI, great when new and properly set up; less good when old & messed with.

John

Link to post
Share on other sites

Hi Andy,

enrichment is needed not just to start, but required until the engine reaches normal temperature. The degree of enrichment required will taper off as the engine warms up. As John says the Triumph set up is designed to give the necessary degree of enrichment for the selected fast idle setting. Using two knobs would work, but will be a lot more fiddly to use than the normal single knob. I can't see that it will give any fuel saving.

Mike.

 

 

Link to post
Share on other sites

Actually, the mechanical cleverness is one of the reasons I've kept my TR6 for 35 years. I love working out why the Triumph and Lucas engineers decided to do things the way they did. It's normally a smart way to maximise the effectiveness without throwing cost out the window. The PI system is a beauty, and a great example of compromise between cost and effectiveness. To make it more fuel efficient you'd need either variable rate springs in the CU, or a custom fuel cam. I fantasise sometimes about making non-linear fuel cams the way Kas Kastner did. But that will remain a fantasy!

John

Link to post
Share on other sites

Thanks all for the explanations.

So just like EFI where enrichment decreases along with fast idle as water temp increases. So with PI and the cams its reliant on you gradually pushing the choke back in as the engine warms up. Not as linear as EFI and as said wear and slack in the system will mess things up I've had everything reconditioned by Neil and have acquired both after market over and under throttle arrangements to try when the time comes.

Thinking Triumph might have considered a single bi metallic strip arrangement to control both cams rather than a cable to give a progressive control similar to some carburettor arrangements.

Overall I'll try the original one knob two cable arrangement. Anyone have a broken one to fix or a used one they would be willing to sell?

Cheers

Andy     

Link to post
Share on other sites
11 hours ago, michaelfinnis said:

Hi Andy,

...... Using two knobs would work, but will be a lot more fiddly to use than the normal single knob. I can't see that it will give any fuel saving.

Mike.

 

 

2 controls definitley does work Mike, there's no question about that. I've had & used both systems for over 40 years and I've come to prefer this alternative, it really is not 'fiddly' at all.

The seperate fast idle is very useful on occasions too, I can temporarily adjust tickover to anything from 650 to 1100 rpm without enrichment being used.

There would be no appreciable fuel saving that I know of but thats not the original reason for the modification.

Bob

Link to post
Share on other sites
16 hours ago, PodOne said:

Thinking Triumph might have considered a single bi metallic strip arrangement to control both cams rather than a cable to give a progressive control similar to some carburettor arrangements.

 

Cheers

Andy     

The Jaguar version of that fitted to series 2 XJ6 was always problematic and very prone to early failure so its probably just as well Triumph didnt use it.

Stuart.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.