New Carb Recommendation

Fuel and Air Systems

  1. bobscuda67

    bobscuda67 Well-Known Member

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    I have a Edelbrock 650 AVS on my 340 and I'm not real happy with it. I know it won't have the performance of a Holley but that's ok. I just wanted something simple and leak free.
    The problem is at idle. I changed to a Comps Cam, XE274, last winter and it doesn't want to idle in gear at all, just want's to stall. I have a 2600 stall converter.
    When I got it running last spring I had to have the idle stop screw turned way in and at that setting I had way to much of the transfer slot exposed. I ended up drilling two .125 holes in the primary throttle blades and I now have .040 of the slot exposed. The idle in park is much cleaner at 900 rpm. I don't know what else to do with it to get it to idle in gear.
    I thinking just to replace it with a better piece but really don't know what to look for. I was thinking about a Street Demon, they look simple and leak free.
    Anyone have any positives or negatives on that carb?
     
  2. OldmanRick

    OldmanRick Well-Known Member

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    Where's your initial timing Bob? The fact that it cleaned up at 900 in gear with your mods leads me to believe that a little more timing may be enough for you? It will never idle like a stocker at 650/750 rpms in gear. I hope a little more timing, if your combo can handle it, will make life easier at the traffic lights for you. :)
     
  3. bobscuda67

    bobscuda67 Well-Known Member

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    I have the initial set at 16* and I'm using manifold vacuum which bumps it up to 22*. That's about the limit as it'll kick back on the starter if I go over 16*.
     
  4. cuda66273

    cuda66273 Well-Known Member

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    Use a 3/32 allen wrench and turn the screw in the vac can clockwise until your idle timing comes up to about 30*. That should help.
    The best thing you can do for that engine is swap the eddy carb for a carb that's suitable for that cam duration and the vacuum signal it's producing.

    Quick-Fuel SS-680Vac is the right carb but you need to change the Idle Air Bleeds in it to get the idle nice.
     
  5. roccodart440

    roccodart440 Well-Known Member

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    If you unplug your vacuum advance and go past 16 deg it won't start?

    You could go with a MSD box with start retard. It retards the timing 20 deg until the engine breaks 500rpm.

    FTR, I'm not a fan of vacuum advance on a performance build. I like straight timing.

    I agree with cuda. the quickfuel or a HP series carb will suit you well. I run a 950 proform and have had great luck with mine but would not recommend taking that gamble. I've heard too much about production quality issues. Stay away from demon.

    I'm not sure which XE274 cam you have (they make 5). YOu may benefit from a little more convertor. I'd get it on a chassis dyno and see where your peak torque is being made. If it's over 2600, I'd do yourself a favor and make the call to PTC, dynamic or the like. What brand convertor are you running right now? Is it a custom or an off the shelf unit. That could be part of your problem.
     
  6. rumblefish360

    rumblefish360 So close, yet so far away FABO Gold Member

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    Hey! It's Don!
     
  7. 65-440

    65-440 Well-Known Member

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    Running a Holley street avenger 770 on my 340, been good for over 10yrs now ! Did a rebuild 2yrs ago ..
     
  8. moe7404

    moe7404 moe7404

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    i think you may have a lean idle circuit. on the AVS, 1968 and latter have a lean idle. i think none of the AFBs did. and may be on the edelbrock. the idle jet is the small brass tube on the pri vinture cluster. only drill one steep at a time. some start at .035-.032". if i find my long instruction set. ill post it
     
  9. Aaron65

    Aaron65 Well-Known Member

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    I accomplished the same thing by using a little ball bearing from a carb rebuild kit to close up the idle air bleed on top of the primary venturi cluster of my 1406. The original size was roughly .052, and I reduced it to .046. I used a small drill to make sure they were equal. This is on a mild Ford 289, but the low-speed circuit was lean, like surge lean, but it would richen out as the main circuit came into line. Some crutch that by going too rich on the main circuit, but that wasn't where my problem was...
     
  10. moe7404

    moe7404 moe7404

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    yep you have a good point. closeing the air bleed is a good way to do it. the real experts do lots of things like that. but i try to keep things simple. i found on 1970 300 H 440 AVS carb, idle jet only needed .001".
     
  11. crackedback

    crackedback FABO Gold Member FABO Gold Member

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    What is the timing when it's in gear. It may be dropping out and you really no longer have what you think.

    An XE274 is not a big camshaft. It should idle pretty easily around 800 rpm with minimal drop in gear.

    Any vacuum leaks? Disconnect EVERYTHING vacuum related and plug it off. Isolate the intake tract and see if you idle changes. If idle speeds changes, you likely have a leak somewhere.
     
  12. Two7T3Dart

    Two7T3Dart ....

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    Using manifold vacuum, maybe your vacuum is dropping too low at idle, thus dropping out your timing
     
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