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Westy

TR4A Sticky Choke Mechanism

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Having managed to successfully sort a few nagging issues with my TR4A (fuel supply, electric fan and overdrive) and now feeling pretty smug with myself, I thought I'd push my luck and try and fix the last remaining issue of a sticky choke mechanism. I have always had to start the car with a good inch of choke but when I push the choke back in, the choke mechanism doesn't return fully without me getting out of the car, lifting up the bonnet and giving it a bit of manual assistance. It's something I have learned to live with, but it's a bit annoying. So I first tried lubricating the moving parts with WD40 - no change. I disconnected the choke cable and checked its operation - all seems to be smooth. But the mechanism itself still has a couple of points where it sticks (fully open and about half open). So as I look at this thing with its return springs, sleeves and levers I am wondering if I should embark on stripping it all out and cleaning and oiling all the parts or whether there is an easier route. Do I have to remove the carbs to dismantle the mechanism? Is there a service kit I should get? Better still, is there an easy fix (I love those best of all)? If it makes any difference I have SU HS6 carbs. Any advice please?

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Edited by Westy
Adding Pics

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Hi Westy,

have you checked the cable for unraveling strands sticking inside the outer cable.   Remove the inner cable to examine properly.

If there are any spring loaded joints in the system take them apart and check for flat spots.

The whole lot should be able to be removed with cabs insitu.  

 

Roger

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I have the same problem on my TR4 for years. In my case it is not what you pictured but it is about the levers underneath the carburettors. A pull on the choke knob means a lever pulls down the needle housing in the carbs. This works well although it needs a firm pull. Pushing in the choke know is another matter - it does not go in far enough. I never could get the levers push up the needle housings back far enough, it always need a manual push home (and then the choke knob would go back home too). This push up / pull down action just has too much friction it seems and I cannot get that to go smoother.
I have replaced the cork seals with Vitron seals, and replaced other things which I thought might help but to no avail. 

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Mmmm....Thanks Roger but it's not the cable as that operates smoothly enough. Badhuis - I did have a look underneath the carbs and watched the lever as I manually operated the choke but I still get the stickiness before the lever starts to pull on the needle (which it does about half way through its arc). So I guess it might be friction between the rotating shaft and sleeve or between the shaft and other bits of the mechanism - but seems strange that it has two distinct sticking points (choke fully out, choke half way). I guess there's only one way to find out. I'm going in....

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Hi Westy,

I too had these problems on my TR4 and made some small adjustments to make it all OK:

  • Make sure the cam is secure and not wobbling side to side on the link bar.  It can catch on the choke screw.
  • Ensure that the connecting lever to the jets does not foul the carb housing.
  • Make sure the gap between screw and cam is set correctly
  • Make sure the cable is pulled through properly so that fully in matches fully closed
  • Check the cable is not too bendy so that it cannot push through any carb resistance.  I changed my solid cable and that helped a lot.

Might help

Mark

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The HS6 setup in the original post is of course different from the earlier SU choke mechanism. I have a set of new HS6 carbs and the choke setup is therefore clean and operates smoothly. I also have a new cable which I shortened to fit in order to reduce the flexing of the cable. I bought the cable from TRF on this side of the pond but I think it is same as commonly supplied. It is also intended to work with the Strombregs and is therefore made long enough to suit that, but too long in my opinion for the HS6. Please see the attached photo. I wanted to duplicate the cable run shown in the Owner's Handbook for the HS6.

To remove the choke shaft it is necessary to remove at least one carb IIRC. The throttle shaft will also want to fall out, its a bit fiddly. Or both can be removed together with the shafts in place, and then separated. I would keep cleaning and lubricating the levers. Look for signs of galling on the brass part of the jets. Ensure that they can move up and down in the jet assembly without sticking. I think they could be lightly polished to improve the action.

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Sorry about confusing the thread. My car has the earlier type of carburettors with a completely different method of choke mechanism.

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Don't forget that the link rod between the two chokes, with the two clamps attached,  has to pivot freely in the choke mechanism securing bolts. If this isn't free, then the choke will stick!

Rich

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Hi Westy, the multi strand cables do not like being put into compression and in this respect are not as good as the solid type. Yours has obviously seen better days as it's well unravelled at the end. If removed from the outer I doubt you could ever get it back but the outer could be too long and is kinking when pushing the knob in.  Get someone to look under the dash when you push it to check if there are any tight bends causing it to move and stop the cable from pushing in.

Chris

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Thanks everyone. I am going to have another look at it over the weekend armed with all your advice and suggestions. On a separate note, I ran the car out to Babington House from Bath tonight  (no, I am not a member) and had forgotten how much fun it is to drive at night especially on a summer's evening. Is it my imagination or do the cars breathe more easily when the air is warm and a little moist?

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Hi, Just thought I'd update you all as I know you're simply dying to know on my success or otherwise. I went through MKTR's checklist and got to the third item to discover that when I depressed the follower screws with my fingers away from the cams and then operated the choke - lo and behold the choke worked smoothly with no sticking. It turned out that one of the clamping screws was loose on the throttle spindle (top right in first photo) and had slipped around so that when operating the choke, the cam was attempting to open the throttle from the "get go" (as our fellow American friends like to say) which required too much effort and so it got stuck. It seems that the shaft is allowed to freely rotate a little first before it gets to the point of operating the throttle as the pin (fixed to the clamped bent arm) is smaller than the slot in which it resides. I wish I knew all the correct terms for the different component pieces but hopefully you get the idea. If someone could tell me what position the screw should be relative to the cam with the choke fully in (e.g. screw in line with straight edge of cam or offset slightly?) I'll then be able to set it up correctly now the mechanism is working. Thanks!

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