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  •  » Explain Edelbrock Carb (AVS2) Design with Primary Jetting Larger?>?>?

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    10/17/2020 9:18 AM  #1

    M1Mustang69
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    Explain Edelbrock Carb (AVS2) Design with Primary Jetting Larger?>?>?

    So Clearly Holley and Edel are VERY DIFFERENT in many ways, but the one that confuses me the most is the Jetting....

    I own an AVS2 650 for my 302 MODDED FB.....(please refrain from replying with TOO BIG, too much carb, why Edel yadda yadda......Im looking for serious responses to serious questions)

    I purchased the Tune kit and have been experimenting, they are interesting to work on/with, but Im finding 1 small change creates Power Surges (assuming Leaner conditions) during Mid-to-Heavier throttling and others are Richer (smellier idles and cruising)........

    it came from the Box with 101P and 98S, Ive gone to 98/95 which was improved odour and mileage with no power loss then Tried 95/98 (with a Holley mentality)......thats when the surges began.  I then played with the metering rods and even with the smallest on the 95 Primary it still had the surges.....clearly 95 Primaries are too small, even at WOT the car felt slightly less Angry than when it was 98/95.........THIS IS WHAT CONFUSES me, how do these circuits work and why wouldnt it be HAPPIER at WOT with the 95/98 Setup???

    (oh and FYI its a Spread Bore, which throws me in even more to a confusion Loop for obvious reasons)

    regards,
    Jeff
     

     

    10/17/2020 10:14 AM  #2

    6sally6
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    From: Surfside Beach,SC
    Registered: 4/02/2013
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    Re: Explain Edelbrock Carb (AVS2) Design with Primary Jetting Larger?>?>?

    What about the metering rod springs?.......You play with those?
    Is it cammed pretty good or stock?   Cu. in.? Fuel pump pressure?
    Modify the ignition curve? (pretty important step in getting-it-just-right!)
    As far as the funky smell....where does you exhaust pipes end??....Rear axle....rear valance...mid car...front of rear wheel..?
    Did you download/read the Edelbrock tune up booklet about how to tune? (it made me scratch my head a little)
    hang in there........we'll finger-it-out
    6sal6

    Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
     

    10/17/2020 10:50 AM  #3

    Bullet Bob
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    From: Montrose, Colorado
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    Re: Explain Edelbrock Carb (AVS2) Design with Primary Jetting Larger?>?>?

    Ok...I'm not going to say a word about the CID of the engine and the velocity of the air passing through the venturi and how that velocity causes  the vacuum due to the vortex of the venturi and how that affects fuel draw through a given jet/rod combination.

    "you get what you pay for, good work isn't cheap, and there are NO free lunches...PERIOD!"
     

    10/17/2020 12:58 PM  #4

    M1Mustang69
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    Re: Explain Edelbrock Carb (AVS2) Design with Primary Jetting Larger?>?>?

    Bullet Bob wrote:

    Ok...I'm not going to say a word about the CID of the engine and the velocity of the air passing through the venturi and how that velocity causes  the vacuum due to the vortex of the venturi and how that affects fuel draw through a given jet/rod combination.

    LMAO well done Captain Passive Aggressive....lol this was great...

    I will answer these engine questions cause they always get asked and although Yes, EXTREMELY important to know for 100,000 reasons, I was asking General Question about Edelbrock, not specific to mine....

    302, Heavier Cam, Edel Performer heads and Intake, Bored over dont know how much, not stroked....also do not have cam specs.....T5 and 3.25 Diff.......

    My General question summerized is "Why Edel has a Larger Primary to Sec Jet Config TYPICALLY, especially on a Spread Bore???  what is going on with the Carb that it needs to see larger primaries even at WOT
     

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    10/17/2020 1:21 PM  #5

    Bullet Bob
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    From: Montrose, Colorado
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    Re: Explain Edelbrock Carb (AVS2) Design with Primary Jetting Larger?>?>?

    I would think that has to do with the use of metering rods which reduce the area of the jet opening...more at light throttle (high vacuum) and less under hard throttle (vacuum drop).

    "you get what you pay for, good work isn't cheap, and there are NO free lunches...PERIOD!"
     

    10/17/2020 3:01 PM  #6

    TKOPerformance
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    From: Newark, DE
    Registered: 12/15/2014
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    Re: Explain Edelbrock Carb (AVS2) Design with Primary Jetting Larger?>?>?

    When you get a surge in an Edlebrock carb your metering is too lean.  Go back one step on the area where its lean (cruise or power). 

     

    10/17/2020 3:27 PM  #7

    M1Mustang69
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    Re: Explain Edelbrock Carb (AVS2) Design with Primary Jetting Larger?>?>?

    M1Mustang69 wrote:

    Bullet Bob wrote:

    Ok...I'm not going to say a word about the CID of the engine and the velocity of the air passing through the venturi and how that velocity causes  the vacuum due to the vortex of the venturi and how that affects fuel draw through a given jet/rod combination.

    LMAO well done Captain Passive Aggressive....lol this was great...

    I will answer these engine questions cause they always get asked and although Yes, EXTREMELY important to know for 100,000 reasons, I was asking General Question about Edelbrock, not specific to mine....

    302, Heavier Cam, Edel Performer heads and Intake, Bored over dont know how much, not stroked....also do not have cam specs.....T5 and 3.25 Diff.......

    My General question summerized is "Why Edel has a Larger Primary to Sec Jet Config TYPICALLY, especially on a Spread Bore???  what is going on with the Carb that it needs to see larger primaries even at WOT
     

    Forgot to Mention, Factory was ORG springs obv and they were bouncing at idle.....so I dropped one to yellow and it was a massive improvement.....
     

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    10/17/2020 3:33 PM  #8

    M1Mustang69
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    Re: Explain Edelbrock Carb (AVS2) Design with Primary Jetting Larger?>?>?

    TKOPerformance wrote:

    When you get a surge in an Edlebrock carb your metering is too lean.  Go back one step on the area where its lean (cruise or power). 

    Thanks TKO, and I know this is the correct way to, well correct it.....This is more of a Curiosity/wanting knowledge question.......Holley TYPICALLY does smaller Primary with a PV and Larger secondaries...........Edel Does LARGER Primary with Metering Rods (act like PV) and smaller Secondaries...I just find it strange that the demand seems to be on the primary circuit, and after I Attempted a 95P with smallest Metering / 98SEC, no matter what I did to the metering rods it always had surges------------But with 98P (varying metering) / 95SEC  although Surgless I could "Smell the richness"

    Its Silly, and well I also think its Dumb they dont seem to make in between Jets for FINE TUNING.....i feel as if a 96 or 97 would be Bang On for my car!

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    10/18/2020 6:39 AM  #9

    TKOPerformance
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    From: Newark, DE
    Registered: 12/15/2014
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    Re: Explain Edelbrock Carb (AVS2) Design with Primary Jetting Larger?>?>?

    I think Edelbrock does it this way to avoid the dreaded bog when the secondaries come in.  A rod/jet system can do a lot more fine tuning than a jet system, because the rod can be designed with a specific taper, etc. to bring enrichment in more gradually.  I think this allows for a more seamless transition from primary to secondary.  They therefore bias it towards the primary, so it acts like a big two barrel until the secondaries are needed and instead of them dropping a ton of fuel all at once instead they can just bring suplemental fuel in gradually.

    If it was just jets you cold always drill the jets slightly larger.  You need some real precision drill bits to do this.  Done correctly it works great.  My father-in-law does this with VW carbs all the time.  BUT, with a rod/jet system this is probably not advisable, because you are dealing with more than just orifice diameter and you may end up with a combination that's impossible to tune as well due to this mismatch.

    In general, even the best carbs are going to be a series of compromises.  The best ones make the fewest trade offs, but if carbs could provide a fuel curve that was as good as fuel injection new cars would still have them. 

     

    10/18/2020 9:07 AM  #10

    John Ha
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    Registered: 4/02/2013
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    Re: Explain Edelbrock Carb (AVS2) Design with Primary Jetting Larger?>?>?

    M1Mustang69 wrote:

     Its Silly, and well I also think its Dumb they dont seem to make in between Jets for FINE TUNING.....i feel as if a 96 or 97 would be Bang On for my car!

    The way it works is the combination of rods and jets - that's how you fine tune.  l had the same concern with my 1400 series and did some charts to help me with the fine tuning - they're posted in the Tips and How-To's forum.  I recently added some for the 1900 series - go here and scroll down.

    There are some "instructions" on the lower right of the first chart I posted that may be useful.
     

    Last edited by John Ha (10/18/2020 9:09 AM)

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