Idle and rev

Discussion in 'Wet behind the ears??' started by Ryanjbill15, Nov 10, 2019.

  1. Ryanjbill15

    Ryanjbill15 Well-Known Member

    when you guys rev your cars does it rev and drop quickly or idle down slowly, mine seems to idle down very slowly compared to most high power applications.

    I have a 71 455
     
  2. flynbuick

    flynbuick Guest

    Too subjective of a question for a worth while answer unless someone posts a video of their tach. What is the condition the tension on your throttle return spring?
     
  3. Mark Demko

    Mark Demko Well-Known Member

    IIRC, SOME vehicles, not just GM, had a throttle "dampner" so to speak, it gently closes the throttle as opposed to it slamming shut after any position off idle.
    What that does is prevent a sudden rich condition from the throttle plates being closed abruptly after being opened.
    I cant recall its exact name, but its on the left (drivers side) of the carb, bolted to the manifold or carb, just ahead of the throttle lever, my '71 GS had one.
     
    TrunkMonkey and BuickV8Mike like this.
  4. TrunkMonkey

    TrunkMonkey Well-Known Member

    Yep.

    Idle return dashpot. Small canister with a diaphragm, a spring and adjustment nut/threaded stud. Carb bell-crank rests on it, when throttle closes, and it provides a slow final closing of the plates.

    upload_2019-12-8_10-1-33.png
     
    Mark Demko likes this.
  5. Mark Demko

    Mark Demko Well-Known Member

    Thanks for posting a pic!
     
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    That can also happen with very light mechanical advance springs.
     
  7. Ryanjbill15

    Ryanjbill15 Well-Known Member

    Did you guys remove this? Any real harm?
     
  8. flynbuick

    flynbuick Guest

    Define “this.”
     
  9. TrunkMonkey

    TrunkMonkey Well-Known Member

    Ryan,

    Is this what you are referring to with RPM returning to idle?




    If so, all the rotating mass on an engine responding like this is way lighter (not to forget, there is no heavy manual transmission flywheel or torque converter on this engine). Anything you have to get moving, requires "effort" to slow down. (hence, the original purpose of a flywheel was to "store energy" to help keep early engine designed running, and running smoothly).

    A small block with an auto transmission, engine accessories is going to rev much slower then the same engine with a high stall torque converter, electric fans and no power steering.

    Small block vs big block, lightened rods, pistons, crankshaft, counterweight knife-blading and polishing, oil scrapers, higher compression have a great deal of effect on how quickly an engine revs and returns to idle, second is induction, heads, cam and timing.

    Most "stock" or mild builds are not going to behave anything like some of the more radical builds.

    But not sure if I am even addressing what you are asking (only that I remember back in the "olde days", guys always trying to figure why their stock or mild built engines did not rap from idle to 8,000 RPM and back to idle in 2 seconds like some guys 289 stroked to 331).

    If this is not what you are experiencing, can you post a video of what you are dealing with? :)
     
  10. Ryanjbill15

    Ryanjbill15 Well-Known Member

    Great reply and thank you very much! What you outlined is exactly what I was referring too.

    I’ll post a video this weekend as well.

    have a great week
     
    TrunkMonkey likes this.

Share This Page