Yes they are reputable suppliers.
A picture tells a thousand words.

Only other thing I can suggest is are they the correct way up? One end has a straight shank and hook, the other a shorter shank and more rounded hook.

That's really the limit of my knowledge and experience on the topic. Hopefully someone else can assist.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

Tried both ways.

They are rubbish now compared to UK originals. Not made same.
Probably Chinese Replacement Auto Parts.

The inner end of the 2 hook wires are just bent, not shaped to a pad.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I watch a lot of FB videos out of Pakistan. I have an inkling a lot of our parts are made directly from scrap steel out of that place.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

You can see on page 27 of the manual gtogreen posted on the other drop test post that the springs are fitted with the circular end of the spring on the throttle linkage. To me that means the shank of the spring is effectively pulling from the centre. If the spring was fitted the other way around it is slightly pulling off-centre and at a slight angle, not directly down. Whether that makes a difference and whether it’s part of your problem I don’t know but from a simple mechanics viewpoint I reckon it makes sense.

Edit: Your pics show the way I’ve suggested is correct with the loop at the top so obviously it’s not the reason for your problem.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

Just to repeat myself, I have tried them both ways round.

PS It is very easy to dismantle the hooks from the springs.

I must have been lucky with the English supplier I used....

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1970 Mk2 Cooper S under restoration

Maybe I have the shield on backwards judging by ausdino's above picture.

The return spring bracket between the two heat shield halves can also go ont two ways - may be worth a check.

Consider SU Midel. They advertise return springs by "Terry's" who were a top spring manufacturer in UK for a long time and made most original equipment for the auto industry. They might still be a quality item.

Here is OLD & NEW. The hooks on the OLD springs don't fall out like the NEW springs.

I am looking for 2 old style springs for my twin SU setup.

Can you not use a standard spring similar to the single su springs?

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Cheers Dave.