Throttle return spring examples

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tiagosantos
Posts: 391
Joined: June 20th, 2010, 12:10 am

Throttle return spring examples

Post by tiagosantos »

I'd love to see some examples.. It's something I've been having trouble with for the past year. I've tried a few different options and they all work to varying degrees, but I don't think I've found the ideal one.

I used to have a spring that went from a plate on the throttle shaft (on the side opposite the throttle cable end) to a plate coming out of one of the carb top's screws. It worked, but it seemed that to close the throttle completely, I needed a very strong spring, so the throttle pedal was a bit too stiff. Using a more moderate spring, the throttle would close partway, but would always be cracked open a bit. I would set my idle to 1100 or whatever, blip the throttle and it would rest at 1500.. If I pulled the throttle back by hand a little bit, it would close all the way and idle where I wanted it to. Maybe the throttle shaft was worn out too much? Didn't seem too bad..

Then I moved the spring to the throttle cable end side, same arrangement - pulling on the throttle cable end, up to the top of the carb. Worked great, but the idle screw interferes with the spring and I worry that it would either catch eventually, or rub the spring until it breaks.

Now I have the spring being pulled diagonally, built a little bracket behind the carb and the spring pulls back and up on the throttle shaft. Seems to work OK, but the throttle cable end arm, where the spring is attached, is pretty long, so the spring needs to stretch A LOT to do it's thing. Also makes the throttle pretty stiff, but I can live with it at this point.

Just curious to see what sort of clever engineering people have come up with.. What I have now works, but I'm sure could be improved.
Veefan
Posts: 247
Joined: August 14th, 2007, 9:22 pm

Re: Throttle return spring examples

Post by Veefan »

You might want to check out your throttle cable. If it has too much resistance or it's old you should replace it.

Just my opinion but controlling the throttle of a race car with a bicycle type cable doesn't sound or feel safe. Over time they tend to wear and in some cases fray or rust on the inside. It’s total over kill but I always use a morse type push/pull cable. Smooth as glass for many years and hard to beat.

Image

http://www.appletreeauto.com/MORSE-SUPREME-CABLE-10/
tiagosantos
Posts: 391
Joined: June 20th, 2010, 12:10 am

Re: Throttle return spring examples

Post by tiagosantos »

The push-pull type cables will also need a return spring, right?

I replace my throttle cable often enough so I'm not too worried about it breaking or rusting - when I bought the car, the old cable WAS rusted through and had tremendous friction. In my car, the cable goes through a narrow piece of steel tubing that's part of the frame. I cleaned it up as best as I could and it feels pretty smooth.. There is a sharp 90 degree corner that the cable goes through (on a pulley), though. I've been told that the cable is too stiff to go around the pulley and that might be causing trouble too.
Veefan
Posts: 247
Joined: August 14th, 2007, 9:22 pm

Re: Throttle return spring examples

Post by Veefan »

You just need the typical dual return springs we already use on Vees for a push/pull cable.
brian
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: Throttle return spring examples

Post by brian »

the key is in the angles. Make sure your spring is located so it will pull in the direction that will finish against the idle stop. Straight up tends to go soft. I use two fairly soft springs in different angles and that will do it. Bicycle cables will work ok but need to be watched for fraying. Do not lubricate cables, you're just asking for dirt to get involved.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
tiagosantos
Posts: 391
Joined: June 20th, 2010, 12:10 am

Re: Throttle return spring examples

Post by tiagosantos »

Ah, a second spring straight up would probably fix it!It takes a very light touch to move it the rest of the way, so yeah, I guess it's all about the angle, eh?

Had a test day yesterday which went well, seems like it's raining this morning so I might skip the practice session (I'm tired and don't feel like changing tires damn it..) so I'll see if I can add a second, softer, spring.
billinstuart
Posts: 201
Joined: July 17th, 2006, 8:53 pm

Re: Throttle return spring examples

Post by billinstuart »

We used a Morse type cable as pictured, with 2 return springs..one at the pedal, one at the carb. No problems after years of use.
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