650 Spread Bore Rebuild Questions

Discussion in 'Holley' started by Brett Slater, Jul 19, 2017.

  1. Brett Slater

    Brett Slater Super Moderator Staff Member

    So, I've decided that (at least for this year) I'm going to keep the old spread bore Holley that was on the car when I bought it.

    It starts and idles great, has good throttle response and I like the "economy" aspect of the smaller primaries/larger secondaries - similar to that of the Q-Jet - which is on the shelf for the time being. I'm very aware that I'd have no trouble getting away with a much bigger carb but in the interest of trying to stop hemorrhaging money, this seems like the most responsible thing to do at the moment. Plus, I'm not planning any trips to New England Dragway, so...

    Anyway, this needs a rebuild, mostly because it's old and the secondaries tend to flood when I come to a stop - which tends to be a PITA. Without feathering the gas, it almost stalls out.

    That said, has anyone rebuilt one of these? I picked up a renew ("trick") kit and plan on attempting this sooner rather than later, as it's the last piece of the puzzle keeping Lord Vader from being unflawed in terms of operation.
     
  2. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    yep . see below - SBB cruiser carb idea .
    I used the quick fuel kit , a bunch cheaper than holley kit . they had a renew kit for that ? which holley kit did you get ?
    pretty straight forward rebuild . take apart slow and inspect as you go . keep the primary side stuff and secondary side stuff in separate boxes or what ever . pay close attention to the choke assy . maybe take a couple clear close up pics with phone for reference .
    if that is a vac secondary carb it does not take the standard diaphragm , needs the shorter version .
    if you let me know the carb "list" number from choke tower I can look in my holley spec book for jetting etc . good to dbl check .
     
  3. Brett Slater

    Brett Slater Super Moderator Staff Member

    It's definitely not a vacuum secondary carb and I don't have access to it right now to get the numbers but I did take a couple pictures a few weeks back. Also, as you can see, there's no choke.

    This is the kit.
    [​IMG]

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    [​IMG]
     
  4. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    Part# for that kit ?
    And FYI that vac port off front metering block is spark advance port . Looks like it is just looped down to front base port .
    I think this dbl pump version with 50cc rear pump could work in your favor .
     
  5. Brett Slater

    Brett Slater Super Moderator Staff Member

    Part number 37-605.

    What about the front vacuum port? Dumb this down for me, please? Haha
     
  6. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    Front metering block port for distributor vac advance .
    I think that should be a #6210 carb . FYI that's $510 new at summit . And I came up with that same kit for a 6210 . $43 .
     
  7. Brett Slater

    Brett Slater Super Moderator Staff Member

    I'll check tomorrow and let you know.

    The kit was $48. Thanks!
     
  8. Stevem

    Stevem Well-Known Member

    Nothing to have any regrets about for only having a 650 cfm Carb as they are perfectly fine for feeding a motor up to some 420 hp and 5200 rpm dependant on the cid!
     
    Brett Slater likes this.
  9. Brett Slater

    Brett Slater Super Moderator Staff Member

    Is that where the vacuum advance should be plugged into??
     
  10. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    yes . that is what the holley book calls it . I used that , seems fine .
    I think they called it a spark vacuum port ? i'll check .
    I think the quick fuel kit part# is 3-206 . not that you need it but ----- info .
    edit 7/24 - finally remembered to check that info - the exact name for that ( in the HP books holley manual ) is " timed spark tube" .
     
    Last edited: Jul 24, 2017
  11. Brett Slater

    Brett Slater Super Moderator Staff Member

    I wonder which port I'm using now. Haha

    Thanks!
     
  12. Brett Slater

    Brett Slater Super Moderator Staff Member

    Annnnd I wonder if that would cause it to break up at WOT....
     
  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Carburetors usually have 2 ports, one is ported vacuum, the other is manifold vacuum. Ported vacuum comes from a source ABOVE the throttle blades. As a result, there is no vacuum at closed throttle. Vacuum rises rapidly as you open the throttle. Manifold vacuum comes from a source BELOW the throttle blades. Manifold vacuum is there anytime the engine is running. Both ported and manifold vacuum will be very close to, if not zero at Wide Open Throttle. At part throttle, manifold and ported vacuum will be the same. It is EASY to tell the difference with the engine running at idle. Unhooking a manifold vacuum port will produce an audible HISS, and the engine will run rough because you just created a vacuum leak. Unhooking a ported vacuum port will have no effect at all, and there will be little or no vacuum at idle. Even leaving it unhooked will make no difference as it is sourced from above the throttle blades. The decision on whether to use manifold or ported vacuum for the vacuum advance can be somewhat controversial as opinions vary. At part throttle, they will produce the same advance. Hooking it to manifold vacuum will give you additional advance at idle. That can help with an engine that runs hot because of relatively retarded initial timing. Pre emissions engines ran manifold vacuum. Later emissions controlled engines used ported vacuum. I tell everyone to try both, then pick the one that feels better.
     
  14. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    No. First thing I would check is float level. Easy to adjust on most Holley carburetors.
     
  15. Brett Slater

    Brett Slater Super Moderator Staff Member

    It should be mentioned that the secondaries were frozen when I bought the car, as some mice had taken up residency inside them. So, it clearly needs the intended rebuild.

    Are the floats on a spread bore as easy to adjust as on a regular Holley? I feel like I've read where they are a bit more involved.
     
  16. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    those are not externally adjustable . have to pull bowls and set to spec . not hard to do , just not as easy as the other style .
    which is one reason I switched mine over to the dual feed style bowls . don't know if that's an easy project with the double pump version ?
     
  17. Brett Slater

    Brett Slater Super Moderator Staff Member

    I guess I'll be finding out very soon.
     
  18. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    Brett , how's the carb project going ?
    So , I've been thinking about the ported an direct vac thing . I have been using the metering block port that we were talking about . This morning I unhooked that , plugged it and ran my vac line down to the lower right side of carb . Seems like it is maybe a little crisper taking off with more initial vac advance . Will maybe switch back n forth to test if I get ambitious .
    FYI , a straight size adapter was needed as the lower Carb fitting was a little bit bigger .
     
  19. Brett Slater

    Brett Slater Super Moderator Staff Member

    I'm on vacation next week and plan on tackling it at some point during the week.
     
    DasRottweiler likes this.
  20. Brett Slater

    Brett Slater Super Moderator Staff Member

    I tore into that Holley today with guidance from my mechanic buddy and made it home without stalling or having to burn off the excess gas because the secondaries flooded out.

    Success!!
     

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