I have a pair of N/A 540s and they start and run great. My question is after running them they will idle high out of gear. Eventually they will slow down to normal idle but takes a while. Both engines act the same. The problem is when you slow down after running and need to dock the engines are idling 1300-1400 out of gear and need to shift (bravos) anyone know what causes this and a cure? engines are 600 hp 620 tq at 4800-4900. 950 quick fuel carbs, 35 degrees timing

it is possible that the springs in the distributors are right on the edge. meaning that they are at full advance but you come down and they are holding the idle up because they are still full advanced. after a short time they start to pull in and the timing comes down and the idle comes down. a timing light will answer that but I have run into it more than once where the distributor was set to bring timing in quickly.

originally i had light springs and the black bushing.now i have the timing locked out . its the same both ways

I used to fix that on older holley by drilling 1 very small hole im each butterfly to let some air by. That would then allow idle speed screw to be set lower allowing idle mix screw to do it job. Maybe not the preferred way but worked for me.

my carbs have a .040 hole in each butterfly.

Sounds lean
You may have to enrichen your idle mix.. The days of achieving high idle with no load on mixture screws changes when low vacuum is present..
In gear dies then we crank up the idle to compensate.
You may need to go up in jet aswell but not sure your combo etc.. Fatten the idle setting then jet if it improves

hot oil thins out and lets the motor run at a higher idle. I see the same issue after a 30 minute run at WOT, a few minutes at idle and all is good

I never thought about the oil. that would be about the right time frame .

it could be the throttle cable adjustment.

I've seen secondary throttle blades hang up just a touch when 'closed' and take a few to work their way correctly closed....1 Holley and several BG Demons.