Odd shaped hole where carb throttle return spring fits

[A TR7 16V]

I have what I think is a MkIII Spitfire twin HS2 carb set on my Herald (the head's MkIII), and I have a problem with the butterfly on the front one (mostly, I think) not returning to the idle position unless I give it a bit of a push. I've eliminated all the possible issues with the cable, etc., and am sure it's close to where the return spring attaches to the lever on the throttle spindle.

I had the carbs off to replace the float mounting rubbers and gave it all a clean and a good coat of looking at. It's all a bit worn of course, but I can't feel any step near the idle position in the movement of the butterfly or any part of the connected linkage. Even assembled, but without the spring, it seems to return to the idle position without any hesitation or extra resistance close to the stop. The only thing I can see is that the hole where the return spring goes in the arm on the carb is oval - well, sort of figure 8 shaped, with a bit of a bump or step between two overlapping round holes. 

Is this the normal shape for that hole or is it wear? They both look the same as far as I can see - though I'm a bit long sighted now. 

If it's wear, and the problem is the spring sticking a little on the bump between the two lobes of the hole, does anyone know where the arms can be got? I've looked on Burlen Fules' webpages, and can't see them, but I'm not sure what their proper name is.

If they aren't available separate or are excessively expensive, what's the issue in drilling the hole very slightly (about 1mm on the diameter) larger to make it round?

The fix I have at the moment is to double up the spring on the front carb. That works okay, but it's a bit tiresome on longer trips as it needs a heavy foot for bigger throttle openings.

Graham

[RobPearce]

I think a photo or two would help enormously with figuring out what you mean!

From your description, the hole shape does sound like wear but I can't see how it would cause any problems. The spring shouldn't be moving within that hole - it presses permanently on one side of it.

[A TR7 16V]

I hope these show the part and what the issue is. 

As to the spring moving, it's more that the hole turns around the hook on the end of the spring as the throttle opens and closes. I wonder if, as the butterfly almost closes, the hook catches on that bump in the side of the hole.

Graham

[A TR7 16V]

While I eliminated the cable and common parts of the linkage, it looks like the fundamental problem is related to the carb return springs not being man enough for the weight of the accelerator pedal at idle, which don't have it's own spring.

So I'm gonna see if that's as it should be with the herald, even the twin carb versions, and see what I can do about it. 

Graham

[RobPearce]

A Mk3 Spitfire would have a pedal return spring from the linkage arm to the chassis. Do you have a solid rod linkage or the later Bowden cable type?

[A TR7 16V]

I've got a bowden cable, but it looks like the link and cable are modified. The bit's in the cabin look v. diff from the parts cat, with the bare cable hanging down from the bulkhead. I couldn't see how to get the cable out at the carb end without desoldering the nipple. So I took the clevis pin out of the actuator arm, and the adjuster, etc. off the manifold. I think the cable inner might come out of the outer if disconnected from the peddle. But I have no hope it would go back through after.

It's all very rusty down on the floor where the spring should be, and looks a little tricky to get at. I've sprayed it with WD40 and we'll see what comes apart without strain later. I note Canley are still dispatching parts, which is really great of them in the interesting times in which we live.

But with the adjuster screwed well in, it seems better. So I might wait till a peddle and bits come on eBay so I have an option when it all goes horribly wrong, like Sod's Law says it will - for them in the US, that's the pessimistic version of Murphy's Law. I like Cole's Law though.

Graham

[RobPearce]

The late Heralds have a very odd looking pedal arrangement. The pedal is hinged at the floor, and this is nearly always rotten (my Vitesse's pedal completely fell off). At the top of the pedal, where the earlier design rested on the drop arm of the linkage rod, the late type just has the Bowden inner cable hooked on the top of the pedal. As the pedal pivots forward and down, this moves away from the hole in the bulkhead where the outer cable is anchored, so it pulls on the cable. The parts catalogue makes it look rather unlike that because it shows the end of the outer in the wrong place.

There should be a spring at the bottom of the pedal, although it's not especially strong. On the 13/60 I had, the other end of the cable operated a lever with a parallel "guide rod" with a proper spring along it. That appears to be fairly well shown in the parts catalogue but is completely different from what you've got.

[A TR7 16V]

That describes the arrangement in the cabin depressingly well except there's no spring (or it's bust).

The situation at the carb end looks to be some ad hoc, spliced together thing. There's an arm on the throttle rod which looks like PN 156290 off the Mk4. There's a clevis pin in a hole close to the rod between the carbs and a U shaped fitting on the end of the cable with the nipple through a hole in the end and the clevis pin through two holes in the sides.

I know I've seen the adjuster online somewhere, but I can't find it now. It's a curved thingy with a long threaded tube that screws in and out of a block pivoted between the two curved arms to take the slack. But neither the u shaped fitting nor the cable nipple would go through the hole in the tube. So I think the inner must have to be unhooked off the pedal and pulled right through to replace it. 

The thing with the pivoted block in it looks a bit like UKC5374, but curved and I think its on the other way round. There's no link rod to the arm on the throttle rod.

Graham

[A TR7 16V]

Here's a pic.

 

[RobPearce]

Hmm... that looks like a bit of a bodge. You'd be a lot better off with the proper late linkage - cable fixed where the bracket touches the breather hose and an intermediate lever, pivoted where your outer cable is attached, with a link rod down to the throttle. That also gives a bit more bottom end progression. I think I've got at least some parts of one in a box somewhere but I don't know if it's all the bits you want.

[A TR7 16V]

I've found some pictures on line of the part I've got, before it was bodged. It seems its the one for one of the Spitfires with HS2s, and is like UKC5374 but with the holes for the carb return springs less far back. I guess I could use UKC5374 with longer springs or spring extenders. But it would be nice to have the proper part number if anyone knows it?

Graham

[A TR7 16V]

If I get a new Spitfire IV throttle cable, will it be long enough for the Herald and will the pedal end fit in the clip at the top of that? I can rescue the carb end clips and bits from the one that's in, but I can't see how they'd fit a Herald cable.

I might replace that nut that has trunnions through the bracket with the pivot arm from a UKC5374 - or replace the whole bracket with one from a Spitfire with HS2s. But then I'm left with that nut on the cable unless I saw a slot in it and risk nicking the inner. Also, it doesn't resolve the issue with a spring under the pedal, which I can get. But am unsure I can fit without it all going wrong and leaving the car US, which I can't let happen at the moment - wife's a key worker and using it, cos she broke her PT and that can't be fixed (if it was worth it) while everything's shut.

But I've got to do some work on the carbs: I replaced the float chamber rubbers, when I had it all apart to replace a bust exhaust manifold. But now it's tricky to start from cold. It was a really good, easy starter, but now, like Rickie Lea Jones wrote "She gets scared and she stalls" (I'd add the next line, but it's a bit of a pejorative in context). I raised the jets to compensate for the float chambers not hanging below the carbs anymore, and checked the mixture from the plugs. But I think I need to set the jet levels properly - 2 turns / 12 flats below level with the step. However, one of the jets is too stiff to come level and turn back. So I mean to pull the carb and clean that better. At which point, replacing the cable and pedal spring would otherwise be a good idea.

Graham

 

[RobPearce]

I think the cable termination at the carb end is correct for some versions but there should be a threaded piece where the kludge is. The top of the bracket has a narrow slot to the hole; you're supposed to slip the inner through that then push the threaded piece into the hole and put the nut on to secure it. As the late Spitfire throttle cable is available, your best bet is probably to get one. It's likely to be the right length, I'm just a little unsure whether the inner extends far enough beyond the outer for the Herald pedal arrangement. If you can find a UKC5374 and something to serve as a UKC3272 then I'd recommend doing so.

I wouldn't meddle with the pedal if you need the car. When I tried to replace that hinge on my Vitesse it turned into a replacement footwell job. The MkIV/1500 parts catalogue shows a supplementary spring from the throttle linkage to the chassis, as on the earlier models. If your pedal feels like it's returning so that the cable has some slack, then perhaps adding that spring will give the return you need. Having the proper intermediate linkage (UKC5374) will compensate for any initial heaviness you get.

[A TR7 16V]

I've a  UKC5374 and UKC3272 and a replacement Herald pedal that's supposed to operate okay, even if hinge is a bit manky, all on order.

I was wondering about getting a length of inner and outer cable and solder on nipples. I've a selection of higher power irons - even got a 12v one somewhere. Wondering if 1m of inner would do, or if I need 1m5? 1m looks less than the one that's on. But that's more'an a bit generous. I might get 2m5 to possibly make 2 and keep a spare in the boot to make sure the one on the car never breaks. I believe strongly that taking an umbrella either stops it raining or makes it so windy the brolly's useless.

I should have all the clips I need and some spares on what's there and whats to come; though I may need a new pedal end clip if they're prone to braking or disappearing when being removed: lost a small nut and washer on the car floor yesterday; spent ages looking; had carpets out and everything; eventually found the bar stewards in me shoe!

Graham

[A TR7 16V]

I've got the bell crank and bracket (UKC5374) fited. It came with a link arm from a 1500 (UKC3272), but that was too long. Luckily I had a link arm on a set of HS8s waiting to go on a Doly Sprint that's just under 2 1/2 inches centre to centre and does the job. What I want (so I can put the stolen one back on the HS8 linkage) is part number 156535. So does anybody have one of them spare?

I think the MkIV link arm might be a little shorter than the one I have on. That has the clevis pin on the end of the cable rather close to the bell crank bracket, and the pin I have is a bit long to go into the slot between the bracket arms - I've a shorter one on order that I hope will fix that better.

I finally found the PN for the bell crank bracket I want from the MkIV, and its 156533. However, the 1500 one used with the HS2s only stretches the carb return springs about 3/8" more than they were. Which is good, as it adds a lot to the return force at idle, but comparatively little at full throttle and is less tiring on the foot than adding another spring in parallel.