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Thread: 4150 vacuum secondaries won't engage & ID help.

  1. #1

    Default 4150 vacuum secondaries won't engage & ID help.

    I have a 4150 with vacuum secondaries. The vehicle is a 1983 GMC 6000 school bus, and the engine is a 366. I tried the paper clip trick and the secondaries are not engaging. When I open the throttle by hand, I can open the secondaries and they move freely. I know I need to take the choke off and get the plunger assembly off the carb, to test the diaphragm to see if it's good. However, I have a couple of items I'd like to identify, if anyone knows what these are. This carb has a governor on it, but the electric connections are disconnected, so the governor should not be working in this case, at least that is what Holley Tech support told me on the phone.
    What is the big part on the left? It's attached by screws to the choke (which is manual), and has the short rubber vacuum hose going from it to the top of the secondary plunger assembly. It also has a coupe of wires on it that go about 5 inches to a T connector. The T connector isn't plugged to anything, and I don't see wiring to plug it to. I've pulled the hose off while engine is running and get not vacuum pull from it or the plunger assembly. The secondary will move freely with engine off and throttle open, and when I plug the connection where this hose goes into the plunger assembly, it still moves freely. Is this extra assembly on the choke something I need to worry about, or just go ahead and test the diaphragm as normal?


  2. #2
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    Quote Originally Posted by bookel View Post
    What is the big part on the left? It's attached by screws to the choke (which is manual), and has the short rubber vacuum hose going from it to the top of the secondary plunger assembly.
    That's the electric governor solenoid that somehow regulates the secondary throttle blades activation.

    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/2800 RPM converter, M4602G aluminum driveshaft, FRPP 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 & 245/45R17 tires.

  3. #3

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    Should the secondaries be opening with this unplugged?

  4. #4
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    I don't know anything about that governor, but I'd start by repairing that wiring/circuit (since it affects the secondary operation).
    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/2800 RPM converter, M4602G aluminum driveshaft, FRPP 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 & 245/45R17 tires.

  5. #5

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    That's the thing; the wire coming off the governor is there with a T-plug. I don't see a wire anywhere for it to plug into. If anyone knows where I'm supposed to be wiring this to, I can do that to complete the circuit, and hopefully get the secondaries opening again.

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