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Thread: Setup recipe for a 390 cfm on a small engine?

  1. #11
    Join Date
    Jan 2010
    Location
    Brisbane, Australia
    Posts
    1,368

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    Hi Brian. Interesting how long the engine "hangs" at a high idle RPM until it settles into a normal cammy idle.
    You have a vacuum leak at the choke hot air inlet near the auto choke housing.
    The richness at idle is part camshaft profile, that you may have to live with.
    I would convert the carb to 4150 style by adding a metering block and longer transfer tube or teed fuel feed line to both bowls.

    My favorite metering block conversion uses the Rapid jet metering block from BLP.
    https://blp.com/cart/index.php?main_...oducts_id=1740

    How are your setting your idle mixture screws, with vacuum gauge?
    What are the camshaft specs, and compression ratio?

    Here's a link to a car like your combination:
    https://www.renaultalpine.co.uk/view...php?f=8&t=7357
    Last edited by Gaz64; 02-25-2019 at 11:47 PM.
    Regards, Gary

  2. #12

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    Thanks for the response. The rev hang in the first video was resolved when I started to make adjustment. I had a vacuum leak in the intake manifold, it was missing a plug. In the other video it does not hang. The cam specs were provided earlier. I have one of these in the vacuum side: https://www.jegs.com/i/Quick+Fuel/79...CABEgI_NPD_BwE

    Mixture screws were set by vacuum gauge. I've been on the RAOC webpage for about 8 years and JL is who first put the Holley on the PRV, at least I believe so. My manifold is a copy of theirs. One primary difference is my head has had a lot of work and has the lofty cam so there isn't any data in that setup. I do appreciate the link you sent because ironically it has the information I'm looking for. So it seems the best idea is for me to review my ROAC notes again and also recheck the manifold to confirm there hasn't been any cracking developing in the intake manifold welds. I don't really have a popping/backfire issue but it will be easy to check. Thanks.

  3. #13
    Join Date
    Jan 2010
    Location
    Brisbane, Australia
    Posts
    1,368

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    Hi Brian. I see your cam specs, not too wild, but up there for a street car.
    Sounds like you are close, you might need to enrich both mains, primary and secondary.
    Stock is around 51 & 59, so you might step them both up a little to say 57 & 66. etc.
    The PV opens at 8.5 and adds the PVCR channel restriction of around 40 in parallel with the primary main jet.
    The QFT metering plate is handy for main jet change, but just check the sizing of the idle constant feed jet in the plate.
    You might also need to experiment with the pump cam and nozzle size. Gary
    Regards, Gary

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