Additional Throttle Return Spring

[jif]

Hi everyone. I’m new here but am after some advice if possible.

I am about to start hill climbing my 2000 NB8A and have been instructed that the stock throttle return springs are not guaranteed to get through scrutineering as a ‘secondary’ return spring is required. I know it’s up for debate whether I actually need to do this but I don’t really want to get to an event and fail scrutineering so I figured that I may as well add another spring anyway.

My question is, has anyone got any advice on the best way to mount another spring? I was thinking of drilling a hole in the throttle body on the arm circled in red for one end of the tension spring to attach. For the other end of the spring, I would need to mount a small plate to the bracket shown with the blue circle. The aim of the plate is to keep the spring attachment point as low as possible so that the axis of the spring does not go over centre when the throttle is open causing the spring to then be acting to keep the throttle open.

Any advice on the best way to do this or even pictures of what anyone else has done would be greatly appreciated.

Thanks!

[hks_kansei]

I'd have thought you'd want to make the blue part higher to keep the spring above the centreline (since the throttle rotates clockwise)

Other than that I can't see any issues with your plan, personally i'd choose the weakest spring I could get away with so the pedal isn't heavier than needed. (if all they want is to see a spring i'd just get some weak as piss thing)



While you're in there, have a look at the throttle cable slack, looks like it may be a bit loose from the pic.
the two nuts on the blue bracket are your adjustment nuts for this. back off the front nut, then use the rear to add or remove slack. then tighten the front again to lock it.

[jif]

Thanks for the advice, I appreciate it. The reason why I was thinking of mounting the blue part lower is because if it is mounted too high, the spring axis actually starts below centre (see dotted line in attached image – apologies about quality) and then when the throttle rotates clockwise it would go above the centreline. It is really hard to find two mounting points that stay above centre.

Another option could be to mount the blue part high like you said and then instead of mounting to the red arm of the throttle body, mount to the one with the green circle.

Do you have any suggestions of the best way to mount a spring to these parts? Do you see any problems with drilling a hole in the throttle body to mount that end?
I completely agree that I will get the weakest spring I can find so I don’t affect the pedal too much!

Thanks for the info on the throttle cable too – I will have to have a look at that!

[greenMachine]

That is a pretty standard requirement, but is oriented at carburetted cars (I am told). In ten years I have never had a problem with either the GM or the racecar, both of which run the standard throttle linkage/spring, and that includes running supersprints at State level and one National level meeting. It's a bit like the requirement for secondary bonnet restraints, on a registered car the standard two stage bonnet release is acceptable.

Who is the organising club? You could speak to their scrutineer, but I would just turn up as is. Worst case, you will be told to fix it for next time.

[hks_kansei]

I'm with green machine in that I think it's an old requirement not needed now (pretty sure MX5s have two springs from factory?)


Regarding the spring position, when you're in there you should be able to work it out, just twist the throttle to full and have a look where the spring sits (use a rubber band or something to work out best position for the mounts, and length of spring)


As far as drilling the throttle, I can't see any issues there.
Just make sure to not press hard with the drill and bend it, and use a good sharp bit since from memory the metal used isn't particularly soft.

[greenMachine]

Who is the organising club? You could speak to their scrutineer, but I would just turn up as is. Worst case, you will be told to fix it for next time.

SDMA at Fairburn Park? Try PMing PeterB, I think he is entered/entering for that one.

[jif]

It's with the MG Car Club in Newcastle. I have spoken to the event contact on the entry form about it and it sounds like it may pass scrutineering but they suggested that I add a spring anyway to make sure. As I haven't done an event like this before, I'm a bit nervous about turning up without one in case they don't let me race.

You're right that they come with 2 springs as standard except the doubt is that because they are intertwined concentric springs they may only count as one.

I forgot to attach the image to my previous post so here it is...

Thanks everyone for the advice so far.

[greenMachine]

Yes, we have all been there, and know how you feel. If you do add a spring, I would use cable ties - simple, easy, cheap.

Good luck, and have fun. I am sure the MGCCN people will make you feel welcome.



PS ... and welcome to the forum!!

[1600Dave]

The "two springs" thing is mainly aimed at old carb'd cars. Some supp regs specifically call this out, and exempt fuel injected cars.

In any event, you have two springs. The fact they are intertwined shouldn't matter - if one fails, the other will close the throttle. That's why Mazda designed it this way. As you have discovered, fitting an additional spring is difficult, having it go anywhere near "over-centre" could cause the very thing the rule is trying to prevent - having the throttle not close properly.

I have had my car (NB8B) scrutineered with MGCCN, no extra spring, no dramas. Obviously doesn't guarantee you will pass, but I would be extremely surprised if it is an issue. They will definitely make you feel at home, great club and great bunch of people. My daughter is currently doing their "Junior Driver Development" course.

[jif]

Thanks again for your help. Cable ties are a great idea so I just need to figure out a way to attach a spring to the throttle body with cable ties so I can just take everything along with me as a backup in case it fails scrutineering.

I'm sure the MGCCN guys will be great - I did a come and try day with them a few weeks ago and they were very nice and it got me hooked!

1600Dave, it's good to know that you've been scrutineered with MGCCN and had no problems. I've checked the supp regs and unfortunately there's nothing in there about fuel injected cars being exempt.

[RS2000]

Hi jif,
I sometimes scrutineer at MGCCN h/c (might have done your car on the Come & Try day) & don't think you will get knocked back without an extra spring. Have yet to see it required on fuel injected cars, especially if road registered.

The Cams manual (General Requirements for Automobiles - Schedule B) states for speed events & races "be fitted with a return mechanism, which in the event of any throttle linkage failure, will close each throttle."

As stated by earlier replies, I think that wording is directed more at carby setups, & the 2 spring NB factory throttle complies in my thinking.
If you do ever need an extra spring, here's some photos of mine (Cams log booked)

DSC02064.JPG

DSC02065.JPG

[jif]

Hi RS2000, thanks very much for your reply and it's great news that you've scrutineered at MGCCN and dont see it as a problem.

For some reason the photos on this thread don't load for me anymore so I can't see how you have added a spring to your throttle, do you know why this is? Is there any chance you can send them through again?

Thanks

[RS2000]

Photos again

DSC02064.JPG
DSC02065.JPG
Cheers