when I was out cruising today every time I came to a stop the idle would come down to 1500 and then after about 30 seconds it would just drop to 1000 where I set it when I set up the motor yesterday or if I bogged the motor by letting the clutch out it would drop and then stay at 1000. I have 2 blue spring in the mech advance, the vaccum adv. is hooked up to manifold vac and doesn't start to pull till 11 to 13 lbs. of vaccum, idle is 9-10 lbs at 1000rpm. the dist. was rebuilt by MSD and the vac adv. is new. total advance is 36 @3000 inital is set at 15, MSD paper work say the vac. adv. is 8 degrees. Thanks for any help or suggestions

I'd guess a vacuum leak. The high idle then dropping back makes me think so.

don't rule out the simple things, throttle linkage and return spring, throttle linkage especially on the non cable cars

mine has done something similar if I come off the highway. It will go to like 1100 or maybe 1200 and in about 30secs finally come down to 1000 where I idle. I have checked for vacuum leaks and just decided that was the way it is? Yours seems a bit more drastic than mine though. I will follow your post to see If you resolution can be applied to mine.

Rick; Disconnect your vacuum advance,plug the port,and I think you're problem will be gone.You can also switch to ported vacuum. Steve

you might be idling on the advance curve, your idle speed has to be lower than the point at which the mechanical advance kicks in.

I started the car up in the garage yesterday and tried to repeat what was happening on Sunday but the car idled fine. I tried switching springs checking with a timing lite when the adv. started to change. one light spring and a blue spring the adv starts to pull right off idle. the heavy spring I have doesn't get to full adv till 5000. two blue springs the adv starts at 1500rpm so I left them in and changed the vac. adv to ported instead of manifold. the linkage is ok. I have to check the valves today and fix an oil leak I found when I took it through the gears at the right front of the oil pan. I took off 1 evac breather and put on a k/n type just incase the motor was building to much pressure inside and the evac breather system wasn't working at a certain rpm range.