Dellorto Idle Variation - S4 Elan

[William2]

I have taken my car out for several trips this weekend and have found that the idling seems to stick at about 1600+ rpm for a while and then will intermittently drop to about 900 rpm or anything in between. I have all the correct return springs on the throttle arm, etc and I am pretty sure that the butterflies are both closing as they should. The carbs have also been rebuilt and thoroughly cleaned with compressed air. Apart from this the car runs very well and picks up without hesitation and plugs are the correct colour on examination. Any ideas what may be causing this erratic idling?

[bitsobrits]

Have you made any changes to the throttle cable routing?

Before I shortened my cable to a more proper (shorter) length, I found that the idle could be affected by how the excess length was constrained with the bonnet on. I.e. the routing apparently increased the cable friction enough to not always allow it to return to idle.

You might try a short run with the bonnet off to see if this changes anything.

[crypto]

Is maybe the choke mechanism loose or sticky ?

[rgh0]

A slow return to normal idle speed can be due to incorrect throttle plate position versus the progression holes. When the throttle is release their is enough of a progression hole exposed to suck fuel through. If the idle speed drops the fuel through the progression hole drops also so overtime it stops and the car just runs though the idle jet hole at the normal idle speed.

Check the throttle butterflys are closing enough to close off all the progression holes at idle.

cheers
Rohan