Autolite 4100 Secondaries Driving Me Nuts

Moms Mustang

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Jun 8, 2015
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I have an autolite 4100 carburetor on a 66 mustang with a 289 engine. I am running the stock intake manifold. When driving the car I feel no response from the secondaries when pressing the gas pedal to the floor. I placed an indicator on the secondary linkage and it never moved when driving the car- pedal to the floor.I have checked the following.

1. Removed the carburetor top, moved the secondary linkage and placed a finger over the hole to the secondary diaphragm. It held vacuum,.
2. With carburetor assembled applied vacuum to the pipe running to the secondaries. The secondary linkage and plates moved.
3. Checked the secondary stop adjustment.
4. Verified that the choke is opening fully
5. Verified the secondary linkage moved freely when the engine was fully warmed up.
6. When I moved the secondary linkage with the throttle open and the engine warmed up (engine off) it appeared to put gas in the engine indicated by a puff of evaporating gasoline.
7. Verified that the gas pedal fully moved the primary throttle plates.

Any ideas of why they are not working would be wonderful. Thanks everyone.
 
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rbohm

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Apr 12, 2002
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there is a spring in the secondary diaphragm that determines how much vacuum is needed to open the secondaries, chances are that spring is too stiff for your engine combination. i would search up a lighter spring. i think holley springs interchange but i am not sure.
 

7991LXnSHO

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Does the spring canister body for the springs come off with a couple of screws like a Holley? If so, the gasket could be shot, they are usually a cork O. Second thought, is the port in the carb body free and clean that provides vac signal to the spring canister?
 

rbohm

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Apr 12, 2002
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it takes the removal of four screws. the secondary actuator looks like a large accelerator pump on the secondary side of the carb. its possible that the diaphragm is damaged, but the OP indicates that is is holding vacuum, so i think it just needs the spring lightened up.
 

rbohm

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Apr 12, 2002
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I also believe that they are. IIRC, the 41 series carbs are Holley pieces.
the 4100 autolite is a ford piece, but i believe they started with the holley design and put their spin on it. there are parts that interchange and parts that dont.

i will say however that the summit carb is in fact a 4010 holley that has been imporved.
 
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