Throttle return springs

[Grumbly]

I have a road rally prepared 1975 TR6 running triple 40 DCOEs. At scrutineering for the HERO Challenge 3 at the weekend, the scrutineer commented that I should have an external return spring for each carb, rather than a single spring acting on the linkage.

As I only now have a clubman's licence, I don't have a current blue book, can anybody confirm this is correct please?

[Drumroll]

Grumbly said:

I have a road rally prepared 1975 TR6 running triple 40 DCOEs. At scrutineering for the HERO Challenge 3 at the weekend, the scrutineer commented that I should have an external return spring for each carb, rather than a single spring acting on the linkage.

As I only now have a clubman's licence, I don't have a current blue book, can anybody confirm this is correct please?

Blue book is available online.

https://www.motorsportuk.org/resource-centre/#year...

[JoelH]

Not sure what that event is classed as but section N 9..3.2 says "Be equipped with a positive method of throttle closing
in event of linkage failure, by means of an external spring to each throttle spindle."

[Grumbly]

Thanks, but section N is auto cross and rally cross, would that apply to rally cars?

[Oneball]

Yes you need a spring on each. J.5.4.2. Is the section.

[dhutch]

Also good practice anyway?

[Grumbly]

Thanks guys, I'll need to find some lighter springs as even with two of the ones I'm using the throttle feel is horrible.

[bucksmanuk]

As a scrute….
The one return spring for each carburettor is the best policy by miles.
The installations that fail (WOT) are almost always the big multiple Weber/SU set ups
I’ve seen 2 fails this year, both ended up as bent cars but drivers thankfully fine.

[Some Gump]

IMO you deffo want independent return springs.

Some time ago, I was in an R300 at Cadwell. The linkage between the throttle bodies went south somehow and result was that 1,2 throttle closed (attached to spring on main assembly) and the other 2 remained wide open. Thank god, it made me go off up the hill at Coppice, not down the hill at the hairpin. No damage (other than some quality time taking some mud out of places mud should not be) and obviously an early bath on the day.

[JoelH]

Grumbly said:

Thanks, but section N is auto cross and rally cross, would that apply to rally cars?

Which why I said the bit about not being sure what your event was classified as.

That section (N.9.3.2) is the only one that explicitly says you must have a spring for each spindle

J.5.4.2 is worded differently for the same scenario (typical blue book) and could be interpreted differently.

Either way I would always run separate springs anyway regardless of whether it was needed under the regulations.

[Grumbly]

It is a robust rose jointed linkage and we've had no issues at scrutineering for the last 5 years, but I'll take your advice and rejig it over the winter.

Thanks to everybody who's contributed.

[velocemitch]

This was one of the first things I learnt preparing my Alfa GTV for road rallying, back in 2006. Weber’s do need the extra external visible spring.
I got away with just one spring for both carbs though, the linkage couldn’t really fail to allow just one throttle to be sprung, the other not, so I think it was fair.

Dellorto’s have a separate external and visible spring, so the rule is covered that way.

Rare to see a TR6 on Historic rallies though, never quite understood why. Maybe that rear suspension doesn’t suit?
Bit like the TR4, being more popular than the 4A ?

[Grumbly]

It's not the most nimble of things to be honest, and ground clearance is a bit of an issue on the tests, but they are robust and reliable.

[Maxdecel]

Distant memory !
I thought the internal spring (#50 in link below) on DCOE's are accepted as one pr. carb and only a return spring is necessary on the linkage? From your description it appears that's what you have.

https://www.carb.parts/?diagram&part=4ab
You'll need two feet on the accelerator with 6 springs working against you

[velocemitch]

Grumbly said:

It's not the most nimble of things to be honest, and ground clearance is a bit of an issue on the tests, but they are robust and reliable.

Robust, reliable and space for the navigator are just as important as being nimble. So it’s got those things going for it.