Question (I think) about mechanical advance distributor and return to idle

[XH29N0G]

I have a question that I think is related to the mechanical advance distributor I have.  When the engine is warm (it was recently rebuilt with an MSD distributor with mechanical advance), the idle settles back down to 900 RPM very very slowly.  I suspect this is just the way it is supposed to behave, but thought I would ask in case it is something else.  If I come up to a light and put the clutch in, it will take its sweet time to get from about 1800 RPM to 1100 RPM and then maybe 10-20 seconds to then settle back down to the idle of about 800-900 RPM.  Is this normal, or should I be looking into other things? 

The engine is 383/452 stroker with a hydraulic cam  (~510-520 lift) and QF 830 carb.  It has an MSD billet distributor and a 6A ignition control. 

It seems to me that before the rebuild, the 383 would drop right back to idle when the pedal was released and the clutch depressed.

Thanks for any thoughts.

[myk]

Someone correct me if I'm wrong, but that's not a distributor issue; rather, I think it's a throttle/linkage issue.  For example, if I rev my engine and immediately let go of the gas pedal/throttle linkage, the carburetor snaps back and returns to idle almost instantaneously.  In newer cars like my '99 F-bird, some idle functions are computer/sensor/solenoid controlled, but in cars like ours it's a simple mechanical setup; after the 'carb linkage is released from an open position it should return to idle almost immediately.

With the car turned off, work the linkage and see if it snaps back right away, and if there's any resistence in the movement.  Also, check your return spring.  Is it set up right?  Is it oriented properly?  Back when I didn't know any better, I put the return spring back wrong and the throttle STUCK OPEN...

[XH29N0G]

Thanks, I will check that.  The return spring that is on the car seems OK, but does not strike me as particularly strong. 

Probably will be a week before I take the car for another spin, but I'll let you know if that solves it.   

[1974dodgecharger]

thats how mine was like Myk said.  I had a small block return spring even though I have a 383 I guess there was  reason why it was its because the big block spring didnt have enough ooomph to bring back to idle set.  So for awihle while I shift that SOB would backfire on me becasue it thought I was still had my foot on the gas while shifting and I dont shift fast.

I realized this when I came to a stop my idle rpm was 1800 I was like WTF.  Did this for a couple more times and then at a 5th stop I pulled the gas peddle back with my foot and the rpms went back to 900 which indicated my spring was not strong enough to bring back to idle speed after I put in the new one.

Its just a remedy though I think I need a new throttle cable actually the stronger spring is a handicap till then.

I put back the 'tougher' spring and then the backfiring and weird rpm jump was gone.

[XH29N0G]

1974dodgecharger,  Can you clarify what you mean by the new spring is a handicap? I gather it has something to do with the throttle cable binding, but am not sure if that is what you mean.  Thanks for the response.

[1974dodgecharger]

1974dodgecharger,  Can you clarify what you mean by the new spring is a handicap? I gather it has something to do with the throttle cable binding, but am not sure if that is what you mean.  Thanks for the response.

yeah the throttle cable is binding somewhere in the line so I need a stronger return spring to bring her back to normal idle.  When I put a new big block spring in its not strong enough to bring her back to normal idle.

I meant the old rusted small block spring is my handicap till I can replace the throttle cable, my bad.