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Thread: SK racing carbs

  1. #101
    Registered User LeonV's Avatar
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    Cool car! Your camshaft, however, is toast and needs to be replaced before doing anything else...
    2/74 260Z

  2. #102
    Nova Scotia,Canada,Earth Blue's Avatar
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    The carb internals seem ok for 1.6 litre. The 50F8 idle jet could be made a bit leaner 50F11 if it runs rich at cruise.

    29mm fuel height is a good initial target. The 115-F11-150 should also be ok for a starting point.

    The 32mm main choke could be dropped to 30 or even 28 to give you more low end.

    Before tuning the carb you need the cam and rocker sorted as well as measure timing.

    Here is a great page that goes over tuning webers: Weber DCOE triples, L28s, and Datsun Zcars
    Last edited by Blue; 05-10-2014 at 02:00 PM.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  3. #103
    Nova Scotia,Canada,Earth Blue's Avatar
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    Here is a Lada racing build with delorto side drafts that may have useful info. Here is a carb bage from the thread: http://forums.finalgear.com/post-you...15/#post856061
    Last edited by Blue; 05-10-2014 at 02:16 PM.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  4. #104
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    Quote Originally Posted by LeonV View Post
    Cool car! Your camshaft, however, is toast and needs to be replaced before doing anything else...
    Thanks, I also think my car is cool I'll fit the old stock camshaft, rockers and springs... then I'll think about buying myself another 316/304. Harder springs had almost no clearance between coils when valve fully pressed (on cold engine after gap regulation), so I think that was the main reason why cam got grinded.

    Hey Blue... amount of Your knowledge is just astonishing. Almost instant replies with just all the valuable information! If I'd live near You I'd buy You a crate of realy good beer for that info!

  5. #105
    Nova Scotia,Canada,Earth Blue's Avatar
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    If I'm in Poland I'll look you up! I have many Polish friends here in Nova Scotia so we should get on well. Keep throwing out questions and all of us on the forum will do our best to help.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  6. #106
    Formerly known as Koalia Reverend's Avatar
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    Haha, a Lada enthusiast in Z site Those little boxy cars show up here now and then. They are the last remains of Communist Soviet Russia..lol

    Speaking about carbs. I've done pretty well with my setup but i wonder could i accomplish a little more in the high rpms by tinkering with jets? I have F11 emulsion tubes, 115 main jets and F9 idle jets... Suggestions? Cant remember the air correctors.
    Last edited by Reverend; 05-13-2014 at 04:17 AM.
    -72 240Z "Goldie"

  7. #107
    Nova Scotia,Canada,Earth Blue's Avatar
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    • Further, it can be taken that the main affects the total range while the air corrector has more and more say as the revs rise, though at no time is its effect negligible.

    • In general, it can be said that large main jets with large air jets give a setting rich in the lower and middle range, while small mains with small air jets achieve the opposite.

    • A very large pump jet or high-speed bleed can enrichen the top-end mixture to such an extent that a larger air corrector may be needed in order to prevent over-richness. This may, of course, in certain contexts achieve the desired mixture slope but, on the whole, large pump jets or opened-out high-speed bleeds making up for the main system weakening off too much in the top range cannot be recommended.

    • Using the same venturi in a 40 vs. 45, the pressure experienced by the charge will increase more in the larger 45 after passing through the venturi and promote more precipitation of fuel from the charge.


    From the great Passini

    So you can have many combinations of main and air that will work for you but having the larger orifice combos are not target to aim for. Likewise you can choke a 40mm and 45mm to the same 30mm venturi but when the fuel/air charge exits the 30mm venturi, it experiences a bigger pressure increase in the bigger 45mm carb throat than in the 40mm carb throat that can cause more fuel to precipitate.

    I have been studying carbs for the past few years and here is where my tuning process has currently evolved to:

    Make sure valves, vacuum/vacuum leaks, fuel pressure, electrical, rings, sealing gaskets, etc. are all in good order. Ensure all carbs are the same with same internal components and are in good order.


    Step A: SET Timing

    1. set ~ 15 to 20 at idle
    2. set ~ 34-40 at max



    Step B: Synchronize Mechanical Linkage

    1. inspect and remove all slop
    2. ensure throttle valves open fully and that accelerator pedal stop is adjusted correctly
    3. set all idle stops for same air flow at idle (800-1000rpm)
    4. set 3000rpm air flow to be the same



    Step C: Disable Cold start system (choke) assembly

    1. ensure cold start plungers are closed and sealing.
    2. disable choke cable mechanical


    Step D: SET Progression and Fuel Bowl Level

    1. get an a/f wideband O2 meter
    2. remove main jet assemblies and close off jet to accelerator pump (at bottom of fuel bowl. A metric bolt will do it)
    3. balance all carb's idle screw mixtures and air flow to get the motor to run evenly
    4. note mechanically where the throttle valves and foot pedal are just exposing the progression holes (cruise)
    5. try to drive around at this "cruise" point in different gears and note the a/f ratio in each gear
    6. adjust the fuel level up if you are running lean at cruise (aim for ~ 14-15 at cruise)
    7. adjust fuel level down if you are running rich at cruise (aim for ~ 14-15 at cruise)
    8. repeat 2 to 7 above until you are happy (check air flow balance and timing). NOTE If you can't get the A/F right at nominal fuel levels then change the idle jets to leaner or richer and repeat steps 3 to 8



    Step E: SET Idle

    1. this is partially done in step 8 above
    2. adjust idle enrichment screw to where you want the idle to be. Most find richer idles ~ 12.5 to 13.5 to be a sweet spot but it can be stinky. If 13.5 to 14.5 works for you then that may be better.
    3. re-check A/F at cruise to ensure the idle progression has not impacted the cruise a/f too much. If it has then change the idle jet accordingly and repeat all of the above.




    Step F: SET Mains

    1. reinstall main jets
    2. make runs on a long gentle incline in all gears from 3000 rpm to 5000 rpm recording the a/f mixture at each 1000 rpm increment
    3. change main jet as required to ensure correct richness between 3000-5000 rpm Target would be 12.5 to 13.5
    4. Once the main jet is selected, repeat step 2 from 3000 to 6500 and note the a/f ratio at the higher end. Change main air corrector accordingly if it starts to go too rich or too lean as you approach 6500. Same target of 12.5 to 13.5 should be aimed for
    5. Recheck cruise to ensure it is not too rich. The fuel height affects were the mains come in. If the fuel is too high, the mains will be in at cruise and richen the mixture. If the fuel height is too low then the mains will come in too late and you will get a lean spot in the transition.
    6. If you can not get an appropriate a/f at cruise (mains in early and too rich) then go back to step D above and lower the fuel level, change the idle jets and repeat the all the fun

    Step F: SET Accelerator Pumps

    1. reinstall accelerator jet at bottom of fuel bowl
    2. make runs on a long gentle incline and punch the gas to accelerate violently and note a/F ratio spikes when you hit the gas and how long it takes to stabilize
    3. repeat in all gears
    4. adjust accelerator pump jet size and fuel bowl back bleed to optimize. starting at lower accelerator jet size is best.
    5. if a lean spot from cruise to rapid WOT can not be resolved with the accelerator pump circuit then raise the fuel level and go back to the drawing board ... STEP D


    Have Fun. It is actually fun and iterative. A good co-pilot reading the A/F and recording in the passenger seat is a must.
    Last edited by Blue; 05-13-2014 at 05:14 AM.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  8. #108
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    I'll get a video of her running. still dialing her in.

  9. #109
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    more pics, video soon.

    [URL=http://s73.photobucket.com/user/akumadc5/media/bay2_zpsd517ac87.jpg.html][/URL

  10. #110
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    well she has almost 1000 miles on the clock with boost and seems to run well for the most part. wot is amazing but cruising is the challenge especially on the freeway, as of now I bought a Little Daily Driver so i can really get some of the kinks out. a new set of 70 idles jets and a wide band 02 along with a 3in down pipe/exhaust are in the near future.

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