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idle vacuum

Discussion in '"Stock" Alpine' started by mightyohm, Aug 12, 2019.

  1. mightyohm

    mightyohm Donation Time

    What's the typical manifold vacuum @ idle for the 1725 with stock cam?
     
  2. beamdream

    beamdream Gold Level Sponsor

    Around 20 - 22" depending on idle speed.
     
  3. Mike O'D

    Mike O'D Gold Level Sponsor

    I have a newly rebuilt 1725 with stock cam - I'm getting 16" at 1000 rpm. If it should be 20" - 22", what else could cause lower vacuum?
     
  4. Barry

    Barry Bronze Level Sponsor


    Retarded valve timing or retarded ignition timing can cause low idle vacuum. Worn rings is a possible cause as is new rings that are not yet properly "seated."
     
  5. husky drvr

    husky drvr Gold Level Sponsor

  6. Mike O'D

    Mike O'D Gold Level Sponsor

    Thanks for the input guys. Timing is 15 - 18 degrees, which is at the upper end of recommended. No PCV - I'm just running a road tube. Valves just re-adjusted "very hot" prior to checking. Brand new Weber carb from SS. New rings not yet seated properly - maybe. I have about 400 miles of pretty moderate driving on it.
     
  7. beamdream

    beamdream Gold Level Sponsor

    Inlet manifold leak ?
     
  8. Mike O'D

    Mike O'D Gold Level Sponsor

    Intake manifold leak would definitely do it, but I have been over that thing with a fine tooth comb. Removed it, carefully inspected it, made sure the mounting surface was flat and true. No gaps when mounted. Got a good tip from a mechanic friend to put a piece of rubber hose on a propane torch and use the raw propane, which can be carefully directed, to check for leaks. No leaks found.
     
  9. beamdream

    beamdream Gold Level Sponsor

    How about around the carb base ?
     
  10. Mike O'D

    Mike O'D Gold Level Sponsor

    Carb has the spacer and 2 new gaskets - well sealed. I plan to borrow my friend's compression tester to see if anything odd is going on there.
     

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