Here's a photo. There are two springs being used in the same location. I fed the springs into each other and connected them.

MS wrote:

Normally, extra heavy springs can cause the throttle shaft bushing to wear rapidly, causing vacuum leaks, but, yours only apply that extra pressure to the pedal linkage, not to the carb linkage itself.  So, if you like it, it should not cause any issues.  In my experience, an extra strong spring makes it hard to maintain constant expressway speeds, but that might just be my personal issue.

Thanks for the heads up on that. I did worry about wear on the carburettor, but as you say, the load is on the accelerator rod.

BobE wrote:

Just an FYI - The National Street Rod Asociation's (NSRA) safety checklist looks for dual springs, and Summit, Jegs, and others sell these dual spring setups. 

Thanks for sharing this. I had heard about double springs being a requirement at certain events. So far I like how I turned my springs into a double, by weaving them together.