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  1. #71
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    Re: Carb Upgrade - S3 Fulvia

    OK, thanks for those replies guys. Good to know we're at least headed in the right direction.

    So that's venturi and throttle barrel size taken care of. I guess that leaves the issue of jetting.

    When I asked the people at Dellorto UK about putting a 27mm or 28mm venturi in the DHLB 32 instead of the 29mm (which is what is in the DHLB 35 version for my car), they sent this:

    "You would need to go proportionally down on main and idle jet size for the smaller venturi compared to the 29mm venturi setting. As a guide the main jet is 4.5 times the venturi size, but if you worked out the the ratio was for the factory setting for the 29mm, and then used that for the venturi that you then decided to use."

    I tried the "4.5 times" formula but it produced results that were inconsistent with the existing main jet/ venturi pairings in the DHLB 32 and 35.

    So I decided to use their second method of calculating the proportionality of the existing main jet/ venturi pairing in the DHLB 35 and applying that ratio to the smaller 28mm venturi to determine the appropriate min jet size.

    To assist with this, I've made up a chart of jettings for the DHLB 32 and DHLB 35 based on the raw data the Dellorto UK people were nice enough to send me:

    (Click image to enlarge)

    Click image for larger version. 

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    *Anyone needing the actual chart for their own use/reference can access the Google Doc I made at:

    https://docs.google.com/spreadsheets...it?usp=sharing

    So I guess what Dellorto UK are recommending is calculating it like this:

    108 (original main jet) divided by 29 (mm original venturi) = 3.72

    3.72 X 28 (mm replacement venturi) = 104.27 (replacement main jet)

    I guess this looks about right because the main jet is 108 in the DHLB 35 with the 29mm venturi and it's 95 in the DHLB 32 with the 26mm venturi

    Here's the DHLB main jet sizes around that size:

    100, 102, 105, 108, 110.

    It would seem the 105 is the obvious choice there being the closest.

    However, I'm keen to know what anyone else may think. Someone may have a different take on it to Dellorto UK.

    In terms of idle jets, these are the sizes available that are within the range of the originals: 35, 40, 41, 42, 43, 44, 45.

    I'm going to be honest and admit I know very, very little about jets and have no experience changing them for tuning etc, so feel free to jump in with any suggestions or advice on other issues around jetting that may need attention.
    Last edited by halejustin; 1st July 2019 at 02:47 AM.

  2. #72
    Legendary Lancista bmarler's Avatar
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    Re: Carb Upgrade - S3 Fulvia

    just one more thought on the venturi calculations. is it the size differential following the venturi that makes the difference? does the incoming barrel size play as important of a role in that calculation? i don't remember if that was discussed. i would imagine it would be important, but is the same formula used?
    i'm only asking as it's fairly easy to increase the bore size and make new throttle butterflies. (depending on the casting your working with anyway)
    bmarler/
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    1961 appia vignale convert.

  3. #73
    Legendary Lancista Marnix's Avatar
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    Re: Carb Upgrade - S3 Fulvia

    Quote Originally Posted by bmarler View Post
    just one more thought on the venturi calculations. is it the size differential following the venturi that makes the difference? does the incoming barrel size play as important of a role in that calculation? i don't remember if that was discussed. i would imagine it would be important, but is the same formula used?
    I'll have to think about that one

    Quote Originally Posted by bmarler View Post
    i'm only asking as it's fairly easy to increase the bore size and make new throttle butterflies. (depending on the casting your working with anyway)
    Nope, you cant, not with the DHLB carbs. You can not turn a 32 in a 35, looked at it, the progression holes are limiting that.
    Lancia Fulvia 2C 1964
    Lancia Fulvia Coupe Rallye 1,3 1968
    Porsche 924 1979
    Alfa Romeo 33 1.4IE 1993

  4. #74
    Legendary Lancista Marnix's Avatar
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    Re: Carb Upgrade - S3 Fulvia

    Quote Originally Posted by halejustin View Post
    When I asked the people at Dellorto UK about putting a 27mm or 28mm venturi in the DHLB 32 instead of the 29mm (which is what is in the DHLB 35 version for my car), they sent this:

    "You would need to go proportionally down on main and idle jet size for the smaller venturi compared to the 29mm venturi setting. As a guide the main jet is 4.5 times the venturi size, but if you worked out the the ratio was for the factory setting for the 29mm, and then used that for the venturi that you then decided to use."
    Tbh, I don't even understand what they are saying... The sentence does not make sense to me


    Quote Originally Posted by halejustin View Post
    I tried the "4.5 times" formula but it produced results that were inconsistent with the existing main jet/ venturi pairings in the DHLB 32 and 35.
    You got to realise that the venturies of the Fulvia are abnormally large (like explained, to get more power out of the engine than could be normally expected, at the cost of rather poor low rev performance)


    Quote Originally Posted by halejustin View Post
    It would seem the 105 is the obvious choice there being the closest.

    However, I'm keen to know what anyone else may think. Someone may have a different take on it to Dellorto UK.

    In terms of idle jets, these are the sizes available that are within the range of the originals: 35, 40, 41, 42, 43, 44, 45.
    You could try that 105. What I would try is to start with the orinal sizes, and see what the engine does.
    As for the pilot jet: since the venturi doesn't play a role in idle and progresion, I think I would leave it as original

    Keep in mind that if you change the main jet, you may also need to change the aircorrector jet.

    Quote Originally Posted by halejustin View Post
    I'm going to be honest and admit I know very, very little about jets and have no experience changing them for tuning etc, so feel free to jump in with any suggestions or advice on other issues around jetting that may need attention.
    Tbh, me neither. I stick normally to the original, assuming that Lancia and Solex have been experimenting with it, and knew what they were doeing, while I half of the time do not what I am doing when playing around like this. One word of advice: may changes one by one, and not all at the smae time. If it turns to run badly, you have no clue really what was right and what was not.
    Lancia Fulvia 2C 1964
    Lancia Fulvia Coupe Rallye 1,3 1968
    Porsche 924 1979
    Alfa Romeo 33 1.4IE 1993

  5. #75
    Legendary Lancista Marnix's Avatar
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    Re: Carb Upgrade - S3 Fulvia

    Quote Originally Posted by Marnix View Post
    Tbh, me neither. I stick normally to the original, assuming that Lancia and Solex have been experimenting with it, and knew what they were doeing,
    Well, in this context, Dellorto actually, maybe - or maybe not - together with Lancia
    Lancia Fulvia 2C 1964
    Lancia Fulvia Coupe Rallye 1,3 1968
    Porsche 924 1979
    Alfa Romeo 33 1.4IE 1993

  6. #76
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    Re: Carb Upgrade - S3 Fulvia

    Thanks for that reply Marnix and sorry for my late reply. I was waiting for some information from Dellorto U.K.

    They've come back with their final thoughts on what jets to use. Here's what they had to say:

    "...I would agree with your main jet calculations (105), its a good size to start with.

    I would keep the air corrector at 200, but you could try something smaller if that is what you have already, as this is going to be a a bit trial and error you need to have a starting point as a reference, then test the engine from there and then make judgements according to performance and spark plug colour, so if you have the 170 in the 32s, try those first.

    For the idle jet try 42."

    Another staff member had this to say:

    "...start with the 29mm (instead of 28mm) choke setting and go down on the main jets as suggested."

    So it sounds like everyone is in agreement that in theory, DHLB 32's should work with the 1.3 engine with some tweaking/ testing/ tweaking and that a good starting point would be:

    Main Venturi at 28 (or 29).

    Auxillary Venturi changed with the more 'open' type from DHLB 35's (they fit) or try leaving the originals first.

    Main Jet at 105 or leave orignal size in there and see what happens.

    Air corrector at either 200 or first try the original 170's that the DHLB 32's should come with.

    Idle jet at 42 or leave as original and see how it reacts


    However, all this will likely cause some clipped top-end performance but come with a trade-off of better low-end performance.

    I guess it makes more sense to first trial as many of the original components as possible to save on what may turn out to be un-necessary spending.

    Any final thoughts on jetting or anything, anyone?


    Last edited by halejustin; 15th July 2019 at 12:36 AM.

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