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  1. #11
    Join Date
    Nov 2004
    Location
    West Sussex
    Age
    62
    Posts
    182
    Holleys are renowned for a stumble off idle as you accelerate. Alan gave me some tips, as did various forums on setting up the accelerator pump linkage and that cured me stumble. Power valves and cam profiles are just for fine tuning the carb. Your vacuum secondary spring should be light yellow, the weakest of all springs for a light car. The stumble is on the primary circuit and most likely the accelerator pump linkage. Settle at your optimum ignition setting before you play with the carb settings. I wasted a lot of time on chasing this fault and I've since cured similar faults on other people's engines with the same carb. Just my offering and I'm not saying I know it all, just sharing my experiences. Good luck.

  2. #12
    Join Date
    Mar 2006
    Location
    Oxfordshire
    Age
    67
    Posts
    1,622
    A good point Ian - it's dead easy to adjust the tickover speed and then forget to reset the accelerator pump linkage clearance.

    BTW, I looked on eBay and couldn't believe what people are charging for the plastic cam kits these days - e.g. this one on eBay. £40 for eight small pieces of nylon! Maybe I should measure up my set and then design and 3D print a few more sets!
    Alan

    CRC Thames Valley Regional Rep
    UK Rep for European Cobra Club (eurocobra.boards.net)
    Dax 427 DeDion - Huddart SBC 383

  3. #13
    Join Date
    Jan 2015
    Location
    Paignton Devon
    Posts
    316
    The more experiences and advice the better, It actually accelerates from idle / part throttle well with no stumble, the problem was trickling along in traffic at a steady almost closed throttle, it would appear I've sorted that but have I really or has the rich idle and big advance just masked it?, I assume I should be able to get a leaner idle than that, it's all a learning curve and I will get there in the end as long as the engine survives all the fiddling!, I've got the Holley spring kit so can try different ones of them although I'm quite happy with the way and when the secondaries kick in, I too couldn't believe the price of the cam kit and being a tightass didn't buy one, I've got a spare carb and a bag of bits with a few spare cams so will see if any of them are different from what I've got

  4. #14
    Join Date
    May 2016
    Location
    Hockley ,Essex
    Age
    56
    Posts
    30
    Hi Roger,
    I am also running a 3.9rv8 in my Cob with similar set up as yours, Holley 390 vac secondaries etc .
    With your reference to timed or full timed ,I use the full timed port which enables engine to idle easily at 750 rpm and goes well straight from idle through to 4500 - 5000 rpm with no hesitation .
    The fuel consumption can also be reasonable giving me about 120 miles for £35 of unleaded petrol,
    If you need any further info ,drop me a line,

    regards,

    Chris.

  5. #15
    Join Date
    Jan 2015
    Location
    Paignton Devon
    Posts
    316
    Excellent Chris, I would be interested in your settings, you can either pm me or email rpm8306@gmail.com, unfortunately during the week I work in an area which has zero phone reception but I can pick up emails or WhatsApp certain times of the day

  6. #16
    Join Date
    Jan 2015
    Location
    Paignton Devon
    Posts
    316
    As an update to this thread, I took the carb off gave it a good going over checked all the settings put it back on, then checked my tdc mark was correct, then reset everything, the result is the car now drives much better, no stumbles at all starts well idles better and will trickle in traffic so hopefully I can leave all that alone now, final settings were
    Primary jet 55
    Secondary jet 57
    28 pump jet
    7.5 power valve
    16hg of vacuum at idle
    Steel vacuum spring
    15' advance at idle no vac
    Vacuum permanently disconnected
    I reckon I could go a bit smaller on the jets but reckon being slightly rich is better than too lean
    Thanks for any suggestions given
    Roger
    Last edited by rpm015; 20-07-19 at 02:15 PM.

  7. #17
    Join Date
    Mar 2006
    Location
    Oxfordshire
    Age
    67
    Posts
    1,622
    Glad you got it sorted Roger - and many thanks for posting the solution update as a nice conclusion to the thread!
    Alan

    CRC Thames Valley Regional Rep
    UK Rep for European Cobra Club (eurocobra.boards.net)
    Dax 427 DeDion - Huddart SBC 383

  8. #18
    Join Date
    Jan 2015
    Location
    Paignton Devon
    Posts
    316
    Cheers Alan, the settings might be of use to someone with a similar engine, as a final edit and end to this, I changed the secondary jet to a 54, but that's definitely the last of the fiddling.............probably....

  9. #19
    Join Date
    May 2016
    Location
    Hockley ,Essex
    Age
    56
    Posts
    30
    Hi Roger,
    I see from your recent post that you are now fairly satisfied with the setup .
    Out of interest what colour pump cam did you use ?

    At the weekend had at a bit of a play with ign timing to see if there was more to gained but found out that increasing to 16 deg was a no go and reduced it to 15 deg .
    The engine seemed a bit sharper with no knock ,the very slight problem was that idle speed would not go lower than about 900 rpm's .
    I will proberbly set timing back to 14 deg at idle .

    Chris.

  10. #20
    Join Date
    Jan 2015
    Location
    Paignton Devon
    Posts
    316
    Chris, I can't remember the cam colour, I didn't change it in the end, I can have a look at the weekend, in regard to the high idle, make sure your secondary butterflies are fully closed and the transfer slot isn't exposed, there is a tiny grub screw under the carb underneath the secondary vacuum which adjusts the butterflies, almost impossible to get to without taking the carb off, I at one stage had the same problem not being able to get the idle down and it transpired the the butterflies were very slightly open, this in turn threw the whole kerb idle/ primary butterfly setting out,
    Hth
    Roger

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