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Thread: Carbs

  1. #11
    Legendary Lancista Marnix's Avatar
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    Re: Carbs

    Quote Originally Posted by TBF-ZAK View Post
    I've found the following settings on the net for the Solex c35
    Thanks for the list. It is quite useful to me, and somehow didn't have this one.

    Take into account that there have been several versions of the C35 PHH. They have a "version number". The version number on the C35 PHH carbs is a bit of a mistery how exactly they have been assigned, but as far as I am aware, they assigned a new version number for each change they made, be it they modified something for a specific engine type, or they had a version for a different engine, or they had a different version for another manufucaturer/engine (like Fiat).
    So not all C35 PHH are suitable for the Fulvia.

    The PHH 3 in the list is a bit of an unknow quantity to me (don't have one, and not seen one in real, so not sure what exactly they are like). The brass tubes giving the fuel enrischment at higher power settings were NOT Always provided in different C35 PHH (for example, the Fiat versions didn't seem to have them). It is possible that the PHH 3 - which seems to be intended for racing applications? - didn't have this standard enrichment feature (and hence could be run with open thrumphets as far as mixture control is concerned). But again, the PHH 3 is unknown quantity for me.

    Quote Originally Posted by TBF-ZAK View Post
    ...
    Quote Originally Posted by TBF-ZAK View Post
    so I'm on bigger main jets.
    But if I understand you correctly, there will be no morefuel due to the drilling. Is that correct?



    Ooops, I am bit lost on this one… Not sure what the connection is with the previuos stuff, and what exactly do you mean by "the drilling"?
    Lancia Fulvia 2C 1964
    Lancia Fulvia Coupe Rallye 1,3 1968
    Porsche 924 1979
    Alfa Romeo 33 1.4IE 1993

  2. #12
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    Re: Carbs

    Quote Originally Posted by Marnix View Post
    Thanks for the list. It is quite useful to me, and somehow didn't have this one.

    Take into account that there have been several versions of the C35 PHH. They have a "version number". The version number on the C35 PHH carbs is a bit of a mistery how exactly they have been assigned, but as far as I am aware, they assigned a new version number for each change they made, be it they modified something for a specific engine type, or they had a version for a different engine, or they had a different version for another manufucaturer/engine (like Fiat).
    So not all C35 PHH are suitable for the Fulvia.

    The PHH 3 in the list is a bit of an unknow quantity to me (don't have one, and not seen one in real, so not sure what exactly they are like). The brass tubes giving the fuel enrischment at higher power settings were NOT Always provided in different C35 PHH (for example, the Fiat versions didn't seem to have them). It is possible that the PHH 3 - which seems to be intended for racing applications? - didn't have this standard enrichment feature (and hence could be run with open thrumphets as far as mixture control is concerned). But again, the PHH 3 is unknown quantity for me.




    Ooops, I am bit lost on this one… Not sure what the connection is with the previuos stuff, and what exactly do you mean by "the drilling"?
    I mean"because the extra fuel is not delivered by the small tubes"

  3. #13
    Legendary Lancista Marnix's Avatar
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    Re: Carbs

    OK, there we go.

    Fuel mixture is delivered from:
    - idle opening, through the idle jet + idle air corrector jet (implemented as a hole drilled in the body) and the varible size jet of the mixture screw. Is active at idle + progession phase, dies out at higher power settings
    - progression holes,
    through the idle jet + idle air corrector jet (implemented as a hole drilled in the body); actually, the idle jet size is not as much important for the idle itself (mixture is detemined by the idle mixture screw, not as much the idle jet size) as for the delivery of mixture in progression. Progression deliver additional mixture up to a certain power level and dies out at higher power settings
    - main power: fuel jet, air corrector jet and emulsion tube, the mixture versus power setting is determined through the combination of these three. For theorie of operation of the main circuit, see a download in download section. Changing any of these will change the mixture. The emulsion tube is particulary reposible for the evolution of mixture versus power, with tuning parameters the diameter of the tube (versus diameter of the well), of holes, their position, and their size. A larager fuel jet will most likely give richer mixture overall, as will a smaller air corrector jet, but it is quite complicated to understand/predict mixture versus power evolution. Main delivery only starts slowly up at a certain power setting, first in addition with the idle and preogression delivery, lmater all on its own.
    - starter circuit: with the starter circuit on, additional fuel is added through the starter fuel jet. Early C32 and C35 had fuel added on all positions of the starter (more air + more fuel), later starter circuits had only additional fuel delivered with the starter position fully open (at intermediate positions only additional air is delivered)
    - acceleration pump circuit: additional fuel is pumped in thrugh the accelearter injectors when the throttle is opened (fuel injected just before the butterfly plates)
    - solex "economat" circuit: the small brass tubes. Additional fuel mixture is added when suction at the input is high enough to draw additional fuel against gravity, through the economat fuel jet (drilled in the body) and mixed with air at the tiny air corrector holes in the head.

    So if you cange the main fuel jet with a larger size, you most probably will get a richer mixture all over the throttle range. The main circuit works independent of that additional fuel delivery at higher power from the small brass tubes (that only give additional fuel at higher power settings)

    Sorry for the long list. But I get so many questions about carb operation that it may be useful to line up all the sources of fuel mixture in the carb.
    Lancia Fulvia 2C 1964
    Lancia Fulvia Coupe Rallye 1,3 1968
    Porsche 924 1979
    Alfa Romeo 33 1.4IE 1993

  4. #14
    Senior Lancista Bart Boosman's Avatar
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    Re: Carbs

    Marnix,

    Are you also able to shine a light on the difference in patterns of holes in the mixing tubes?
    There are so many different patterns, all seemingly original: 4 holes at right angles in the middle of the tube, a row of holes over the length of the tube, one side only or drilled through, bottom open or closed, etc.
    I had 3 sets of 42ddhf's, and the holes in the tubes in all 3 were completely different.

    Long ago I experimented a lot with these tubes and found distinct differences between the patterns, but usually an improvement in one way was countered by a disadvantage in another. (I subsequently made a fuel injected manifold which solved the problem of correct mixture quite effectively)

    Bart

  5. #15
    Legendary Lancista Marnix's Avatar
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    Re: Carbs

    Quote Originally Posted by Bart Boosman View Post
    Marnix,

    Are you also able to shine a light on the difference in patterns of holes in the mixing tubes?
    There are so many different patterns, all seemingly original: 4 holes at right angles in the middle of the tube, a row of holes over the length of the tube, one side only or drilled through, bottom open or closed, etc.
    I had 3 sets of 42ddhf's, and the holes in the tubes in all 3 were completely different.

    Long ago I experimented a lot with these tubes and found distinct differences between the patterns, but usually an improvement in one way was countered by a disadvantage in another. (I subsequently made a fuel injected manifold which solved the problem of correct mixture quite effectively)

    Bart
    Hi Bart

    I think the emulsion tubes are about the most tricky part of the whole carb setup. They essentially regulate the mixture setting versus power. The (simple) theory is explained in that download section document. But how many holes, how large diameters, how high the holes positioned, open or closed at the bottom, even the diameter of the emulsion tube versus diameter of the well are all parameters. I don't have a clear tekst on how to tune really.
    Tuning maunals usually refer to diffrernt types of emeulsion tubes that are made available by the carb manufacturer (like Weber and Dellorto), but I still have to come accross a manual that explains exactly how and wehre to provide holes in the emulsion tube.

    For the C.42 DDHF (except maybe the very early samples): 4 crossholes somewhere along the middle of the tube, with end closed off is the correct type. Note that there are 1mm washers under the air corrector screw to raise the emulsion tube slightly upwards. I have seen tuners soldering shut two of the four cross holes.

    The ones with many holes, single line, is for the C.32 and C.35 carbs. I have seen these fitted to DDHF carbs, and I dount they run well.

    PHHE carbs have open ended emulsion tubes.

    I can only vaguely explain what they did:

    - for the C.32 and C.35 fuel economy was most likely and import argument, so they provided many (smaller) holes to gradually counter the enrichment with higher airflow. The idea is to keep the mixture over the whole power range quite lean (with fuel enrichment at highest power with the "economat" enrichment).
    - for the DDH, the fuel economy was maybe a bit less of an issue, but richer mixture was (cooling). They basically provided one large single step in countering the fuel enrichment with higher power, with the four big crossholes giving a quite nig "re-leaning" step somewhere in the middle of the power range.

    That basically what I can contribute so far. I am not involved in tuning really, and I haven't experimented with different configurations. What you say is not a big surprise: configuring carbs is Always making some kind of optimal compromise, and if you improve something you almost always pay a "price" for it in that some other parametr going "down". I just get carbs in the best possible state according to factory specs, and then they run quite well...
    Lancia Fulvia 2C 1964
    Lancia Fulvia Coupe Rallye 1,3 1968
    Porsche 924 1979
    Alfa Romeo 33 1.4IE 1993

  6. #16
    Legendary Lancista lancialulu's Avatar
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    Re: Carbs

    To add to this (as I am also interested in modifying the emulsion tubes), I run DDHF40's on my 1.3HF.

    When I got the car it ran quite nice (with the obvious "hole" around 2000rpm due to the large choke) but the carbs had a mix of jets including a standard C35 PHH 180 air correction on a PHH multi hole emulsion tube (ie 3 pairs of holes from centre up ** correction from the centre down**).

    I acquired a set of correct 140 air correction jets fitted to a standard DDFH emulsion tube (4 holes in the centre). When I fitted this tube the car ran very badly with such a much larger hole.

    I am thinking to fill the "hole", a better transition from the idle circuit to main jet is required. I assume the progression ports are not really modifiable (I do not want to machine these carb bodies)?

    I upped the idle jet to 60 which made some difference to the PHH emulsion tube set up but not to the DDHF tubes (still a big hole).

    I would be interested to see Bart's analysis of his tube variants.

    According to the DellOrto tech book an emulsion tube like the PHH multi hole is used to enrich on full throttle which seems to be what I am experiencing when compared to the DDH tube which DellOrto do not have that option in their book.

    What is the relationship between fuel flow, aircorrection jet size, and throttle position wrt to engine speed??? Answers on a postcard....
    Last edited by lancialulu; 13th August 2019 at 11:50 AM. Reason: mistake in defining the PHH emulsion tube

  7. #17
    Legendary Lancista Fulvia-hf's Avatar
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    Re: Carbs

    When I fitted DDHF42's to my 1200HF engine it proved a pain to set up the mixture correctly as there is no known set-up to start with. To make matters worse the fact that you have to remove the carburators to be able to change the mains is a pain. I was able to have somebody modify my carb bodies ( as an experiment) to take Weber DCNF mains and air correctors stacks from the top. (just under the float chamber vent lid). Apart from being able to change jets much quicker there is also more choice in emulsion tubes. The DCOE has much more options to choose from but the DCNF has if I remember correctly about 7 different types. Reason to go for DCNF over DCOE jets is a space issue. A DCOE stack is much taller and won't fit.
    After a rolling road session I had maximum power 119Hp but it proved undriveable. After fiddling with several emulsion tubes I ended up with F30 and I think 135 mains.

    Cheers,
    William
    Last edited by Fulvia-hf; 14th August 2019 at 03:32 PM.

  8. #18
    Legendary Lancista lancialulu's Avatar
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    Re: Carbs

    Hi William

    An F30 has central cruciform of holes and a cruciform of holes midway above this. According to my weber data this give slight enrichment at low revs (which is what I would expect you would need to fill the "low speed flat spot"). However the position of the emulsion holes above the centre is counter to the dellorto equivalent which has holes below for the same purpose. Is this correct??

  9. #19
    Senior Lancista Bart Boosman's Avatar
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    Re: Carbs

    Tim,

    For experimentation, I closed holes with a drip of epoxy. I didn't notice much difference in bottom open or closed, but (as you also found out) holes over the length of the tube make a big difference. With holes in the middle of the tube only, float level is very critical.
    But, like I said before, I couldn't get it right enough for my liking and went to Iniezione.

    By the way, carb installation is much quicker if you tap M8 into M7 nuts which require a 11m socket which just fits in between the carbs and make assembly so much easier.

    Bart

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