Who's the IDA expert ???

Im having problems with revs holding and then dropping
down slowly,do ida"s have an internal spring like dcoe webers,when broken causes this.

are you sure you don't have a manifold leak ? Sounds like it maybe sucking air.

Dutchy,
IDA's are very basic therefore no internal springe except for the accelerator pump springs (one on the cam and one on the pump)
What have you checked so far?
As a suggestion, check the following things
Air leaks in the manifolds etc.,
Linkages to the carbies and their synchronisation with the carbs,(this can be done by removing a linkage at each carb in turn and observing any movement back to idle by the carb. linkage arm. If no movement, see if the idle drops by pushing each linkage arm towards the idle position
a distributor advance curve that is advancing too quickly, thereby holding a higher than normal advance (and RPM) when returning to idle
Regards

have you played with the throttle shafts or butterfly plates may be there binding slightly

Thanks guys ive got a bit of checking to do.