Stromberg throttle springs

[Lambo911]

Hi,

I've been having trouble with the idle speed hanging on my S3 V12 when hot, it has four Stromberg 175 CD2SE. When I push the throttle lever on the carb back closed it goes back to the correct idle. I only need to move it a fraction, probably less than 1mm. Seems to be the front left and right rear that are causing the problem.

Do the small throttle springs (part 12844 on SNG Barratt) lose their springiness over time or could it be something else like an incorrectly set butterfly?

Cheers

[Doddsy333]

Richard, I have exactly the same problem as you mention. My Series III also doesnt return to idle when hot. Did you manage to find the cause? Did you change the return springs?

Ive been sorting out the tuning of my car and it is now running very well but after an hour on the motorway it was taking a good few seconds for the revs to slow down after taking my foot off the throttle and the idle speed was a lot higher circa 1100.

I have rebuilt my carbs. I was wodering if the new throttle spindle seals could be a cause.

[Lambo911]

Hi,

I just bent the springs round and it works perfectly now. They'd just got tired over 43 years so they needed a tweek!

[Robert Hiland]

Yes, over time the springs do loose strength. Some mechanics suggest preloading the spring by rotating (tightening) before you install. 1/2 turn should be sufficient. Check the relative tension on all return springs to ensure an positive return.

I have a 4.2L engine with 3 SUs. The spring closest to the firewall is longer than the other two due to the configuration of the mounting bracket. Would this also be the case with your engine?

[Lambo911]

There is only one spring listed for the V12 so I assume they are all the same.

The spring is part of the Stromberg, it's a round one that goes around the throttle spindle so it should be standard for that particular carb.