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Thread: The infamous off idle surge

  1. #1
    Keithm1 Guest

    Default The infamous off idle surge

    OK, here's the setup. It's an 1850-2
    Stock Ford 302, Edelbrock 2121 intake, 15" of vacuum
    6.5 power valve, 25 squirted, 66 main jets
    Idle mix screws at 3.5 turns

    Idle is a little shaky. When accelerating engine is smooth and strong. Just off idle it surges bad, I've tried timing to no avail.

    I've read a bunch about surging but no one seems to have a solution. As little as I'm on the throttle when the surging occurs I would think that it hasn't transitioned from the idle circuit to the mid range yet. Problem is, richening the idle circuit doesn't seem to help, neither did leaning it. Any ideas? Keith

  2. #2
    Join Date
    Dec 2009
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    23,427

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    Quote Originally Posted by Keithm1 View Post
    Problem is, enriching the idle circuit doesn't seem to help, neither did leaning it. Any ideas?
    Often times, a lack of ignition timing advance is what causes this.
    Before disregarding timing (as so many do), read pages 4-10 of this Edelbrock EFI tuning manual, it's very good:
    https://edelbrock-files-v1.s3.amazon...ers-manual.pdf (EFI related, but still applies to carbureted engines.)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & MT 245/45R17 tires.

  3. #3
    Keithm1 Guest

    Default

    That is some great reading. It does bring up the question of the vacuum tap on the metering block, should I use that with the Ford engine?

  4. #4
    Join Date
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    Connecticut
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    Quote Originally Posted by Keithm1 View Post
    It does bring up the question of the vacuum tap on the metering block, should I use that with the Ford engine?
    If you have a vacuum advance distributor, absolutely use it!
    8°-12° of additional vacuum advance is the typical limit (adjust).
    Connect the vacuum hose to a full manifold vacuum port.
    The timed spark port (metering block) is only for emissions/EGR engines.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & MT 245/45R17 tires.

  5. #5
    Keithm1 Guest

    Default

    OK I went back in and reset the timing, static was 12 I have moved that 20, there is no change whatsoever, I was able to take it out on the road for a long steady run. As long as its accelerating it is smooth and strong. If at any speed you hold the speed steady, it surges at higher speed the surge is weaker but still noticeable. I'm thinking of larger mains, but is there an overlap from the main circuit down to mid and down to idle. This is the first round I've had with a Holley and I have to say it has been a pain, I've always used AFBs and Webers, never had this much of a problem dialing out a surge. Keith

  6. #6
    Ryan Guest

    Default

    Having exactly the same problem. But I'm not running any vacuum advance. Someone please hit me up if you figure something out. Much obliged.

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