Engine idle speed staying high

[JMD]

Hi Folks
I seem to have an issue with my 1963 3.4 MK2.
When I have the car in driveway with engine idle at 750rpm and I raise it to 2000rpm then release throttle pedal The engine speed falss back to the set 750rpm as normal, However, while driving the car this is not the case. The engine speed sits sometimes 1000rpm to 1500rpm and only comes down if I blip the acelerator pedal. Could this be some sort of vacuum leak ?

I have confirmed the twin carbs linkage is tight, I even slackened off and confirmed butterlys were fully closed at engine off.

I recently had the carbs overhauled and a 123 distributor fitted at same time.

[mike020150]

Engine vacuum leaks would result in a permanently high idle speed, so once you have eliminated all the possibilities of stiction in the throttle linkage, it would be worth checking carburettor needle centralisation and the cleanliness of the dashpots. Mike.

[JMD]

Thanks Mike


I still have issue. Took another look at the carb linkage. The front carb has a spring that is a failsafe to ensure that the butterfly returns in the event that the connecting linkage comes loose. Well thats what Im assuming..

This front carb return spring seems to be fowling on other parts of linkage. Maybe its supposed to be routed this way but if someone could post a picture of their own front carb return spring I might have found the issue.

I have posted a couple of pics of this