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Technical holley 600 vac. secondary issue.

Discussion in 'The Hokey Ass Message Board' started by 26 T Ford RPU, Nov 21, 2020.

  1. I have a #1850-2 600 vac. secondary carb on my 301 Chev in my RPU.
    The issue is the secondaries have never worked. The T is around 800 Kilos or about 1700 lbs and runs a power glide and 3.78:1 rear.
    I have done the paper clip thing on the diaphragm rod and nothing, put the lightest spring in and still nothing. The carb was new to this motor and has done less than 5K. It runs strong until the primaries max out.
    It does 80mph in the 1/8th miles and only 90 in the 1/4 but sometimes when i get off the gas the secondaries give a kick but only then and for split second.
    The set up:
    301 Chev,
    @11:1 compression.
    Edelbrock Street Master intake with home made plenum divider.
    Power pac heads. 1.7 intake valves
    Cam is a Std 400 Chev item.

    I have googled this and there is a test you can do with compressed air but mine does not have that little port they show. I have not put a vacuum gauge on it.. i don't have one yet.

    So, any suggestions before i buy a new carb?
    It does run very well for only being a 300 cfm carb but where is the fun in that.
    Cheers, JW
    [​IMG]
     
    Last edited: Nov 29, 2020 at 5:53 PM
    Deuces likes this.
  2. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 2,743

    2OLD2FAST
    Member
    from illinois

    Have you done any disassembly ? Any testing ? Do you have access to a vacuum pump ?did you check the linkage to make sure its free and not binding ? Tell us what you've done ..
     
  3. I have checked the linkages and are all free. as i have said i have not done any vacuum tests. The only disassembly i have done is to change the diaphragm spring. There was no change. Iwill get a vacuum gauge soon and test that. there are no leaks. JW
     
  4. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 2,743

    2OLD2FAST
    Member
    from illinois

    If you haven't removed the diaphragm canister from the carb , how do you know there are no leaks ?
     
    Last edited: Nov 21, 2020
    hemihotrod66 likes this.

  5. I did remove it, i changed the spring as i said. JW
     
  6. onetrickpony
    Joined: Sep 21, 2010
    Posts: 444

    onetrickpony
    Member
    from Texas

    On a light car like yours, the secondaries may not fully open. Try disconnecting them and run it. You may find that they are opening, just not real hard.

    I have run into issues a couple of times where the link on the throttle side that closes the secondaries is not adjusted correctly, keeping the from opening all the way.
    I'm not familiar with the paper clip trick. Is that like putting a screw in the linkage to force the secondaries open?
     
    26 T Ford RPU likes this.
  7. Automotive Stud
    Joined: Sep 26, 2004
    Posts: 4,129

    Automotive Stud
    Member

    I think it's time for mechanical secondaries.
     
    irishsteve and 26 T Ford RPU like this.
  8. Deuces
    Joined: Nov 3, 2009
    Posts: 18,748

    Deuces
    Member
    from Michigan

    The paper clip idea works great.... I've done it before to find out if the secondaries are working properly.....
     
    egads, mad mikey and 26 T Ford RPU like this.
  9. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 2,743

    2OLD2FAST
    Member
    from illinois

    You don't need a gauge , you need a pump to apply vacuum to the canister ( while removed) to check its operation , or push the diaphragm rod up & put your finger over the hole to see if it holds position , if it does not , the diaphragm is leaking . next run a piece of wire through the carb vacuum orifice to be sure its clear .How many rpm are you revving the motor to to test ?I have no way of knowing how much you know or what you've already done . When someone offers help , why argue ?
     
    iwanaflattie and dirty old man like this.
  10. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,689

    dirty old man
    ALLIANCE MEMBER

    There is a check ball in that diaphragm chamber, make sure it isn't stuck in it's seat.
     
  11. scrappybunch
    Joined: Nov 16, 2011
    Posts: 327

    scrappybunch
    Member
    from nj

    Wrap a small zip tie around the shaft of the diaphragm, and push all the up. Test drive, and see how far the shaft moved.
     
  12. ottoman
    Joined: May 4, 2008
    Posts: 288

    ottoman
    Member
    from Wisconsin

    Is the small cork sealing ring between the canister and housing good? And is the body passage open to the primary bore?
     
  13. Thanks for the replies.
    The suggestion of the paper clip on the diaphragm rod as well as the zip tie, done it and it did not move.
    When i had the canister off to replace the the diaphragm spring i made sure the little cork seal was good.
    I see that i will now need to remove the canister and check it works on the bench with a vacuum pump and check passages.
    One check i will do is put a small nut and bolt in the linkage and see if the secondaries do work in a mechanical fashion.
    RPM, 2800 @ 60 mph. I have tries full throttle on hills for lower manifold vacuum, nothing!
    The suggestion of time for a mechanical secondary carb....thinking about it if i cant sort this one.
    The one thing in the back of my mind is the car is light and may not get that low in vacuum.

    If i have time today i will pull the canister and check/ test.
    Cheers, JW
     
  14. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,689

    dirty old man
    ALLIANCE MEMBER

    I don't claim to be an expert on Holley (or any other carb), but I believe the diaphragm is actuated not by lowering manifold vacuum , but by venturi vacuum created by airflow thru the venturi, with an increase in rpm increasing air flow and vacuum to actuate secondaries.
     
    arkiehotrods, ottoman, Deuces and 7 others like this.
  15. I'am no expert on them also, Dave. I do believe you may be correct and as i have said my carb doe's not have the little port above the venturi that was shown in the fault finding video. JW
     
  16. sdluck
    Joined: Sep 19, 2006
    Posts: 2,526

    sdluck
    Member

  17. Tickety Boo
    Joined: Feb 2, 2015
    Posts: 1,156

    Tickety Boo
    Member
    from Wisconsin

    Had this problem on a 750 V/S, the diaphragm was old and brittle, so when took the cover off to change springs it never sealed again, replaced it with a new soft one :oops: While apart also installed a Holley quick change spring kit #20-59 ;)
     

    Attached Files:

    Last edited: Nov 21, 2020
    26 T Ford RPU, mad mikey and Deuces like this.
  18. I am going to replace the diaphragm while i have it apart. JW
     
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  19. jaracer
    Joined: Oct 4, 2008
    Posts: 520

    jaracer
    Member

    You say you don't have the venturi vacuum port, if that is so, the secondary's will never work. However, I do believe the carb does have that port, it's pretty small. The attached diagram will help you find it. It is probably blocked with dirt or varnish. vacuum sec.jpg vacuum sec.jpg

    Air rushing through the right primary bore will eventually produce enough vacuum to pull up the diaphragm and open the secondary's. As they begin to open, air rushing through the secondary's will help pull the secondary plates wide open.
     
  20. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 2,743

    2OLD2FAST
    Member
    from illinois

    Excellent info , far better than lots of words !
     
    61Cruiser likes this.
  21. scrappybunch
    Joined: Nov 16, 2011
    Posts: 327

    scrappybunch
    Member
    from nj

    Remove the housing and blow air into the feed port. It should come out both of the ports in the venturies.
     
    seb fontana and 26 T Ford RPU like this.
  22. jimmy six
    Joined: Mar 21, 2006
    Posts: 7,188

    jimmy six
    Member

    Don’t do the nut and bolt thing on the rear linkage without disabling the vacuum canister. You put washers under the diaphragm. If you don’t the back barrels will stay wide open and blow your engine if you don’t turn it off. If your out driving you will probably injure yourself.,
     
  23. 1971BB427
    Joined: Mar 6, 2010
    Posts: 5,895

    1971BB427
    Member
    from Oregon

    If the little seal between the main body and the vacuum diaphragm is not sealing, the secondaries wont ever open. You do need to put a vacuum pump on the carb to see if you can pull a vacuum, and then open the throttle to see if the secondaries also open with vacuum applied.
    The secondaries should open some, even if no vacuum, when you open the throttle fully. So might check to see if that works also.
     
    26 T Ford RPU and Deuces like this.
  24. It gets full throttle from the pedal and have just checked for the port at the R/hand venturi and can not see it, even with a spot light and reading glasses. I also held the throttle open and did the compressed air test and nothing although i now know for sure fuel comes out the secondary discharge tubes. If it stops raining i will do a short test drive on a quiet country road and do the nut n bolt in the secondary and i have taken precautions that it can not lock on. Next will be to pull the diaphragm canister and do the tests on that but i am concerned that there appears to be no port in the primary venturi. JW
     
    Last edited: Nov 21, 2020
  25. Tickety Boo
    Joined: Feb 2, 2015
    Posts: 1,156

    Tickety Boo
    Member
    from Wisconsin

    The primary port is not much bigger than a pin hole :rolleyes:, it is hard to find with out taking the carb off and looking close, compressed air chuck needs to be held right next to it while throttle blades are open enough to free the secondary's to open, linkage is designed to mechanically close secondary blades near idle.
     
    26 T Ford RPU likes this.
  26. Throttle was wide open during the compressed air test and i went over every bit of the rear of the primary venturi. JW
     
  27. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 2,743

    2OLD2FAST
    Member
    from illinois

    I'd be very surprised if you could get enough volume of air forced through the venturi with sufficient velocity to open the secondary . Looking down from in front of the carb , the TINY port is at about 10:30-11:00 o'clock , down 3/4" , secondary port is straight to the rear , it takes both ports working , the frt begins the process , the increased signal from the sec. does the heavy lifting. There is no sec. Signal until the sec. Flaps begin to open .
     
    Last edited: Nov 21, 2020
  28. Tickety Boo
    Joined: Feb 2, 2015
    Posts: 1,156

    Tickety Boo
    Member
    from Wisconsin

    Best guess is that the diaphragm is leaking or the port is blocked
     
    hemihotrod66 and 26 T Ford RPU like this.
  29. The compressed air test was taken from a Holley site on the interweb. i will know by tomorrow (NZ time) and all going to plan what the issue is. JW
     

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