You have a 1966 Mustang 6-cylinder with a Holley 1940 carburetor.
You have spark, fuel pump is new, fuel is reaching the carburetor inlet, but no fuel is getting past the needle and seat — so the bowl stays bone dry.
What We Know
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Fuel line to carb = good.
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New pump = good pressure.
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Needle and seat = fuel should flow when the float drops.
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Bowl stays dry = fuel is 100% blocked at the needle and seat.
Most Common Reasons for This Exact Issue
Stuck Needle
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Even a new or clean needle can stick tight in the seat, especially if the float doesn’t drop freely to pull it open.
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The viton tip can stick if there’s a burr or the float tang isn’t pushing down far enough.
Float Installed Upside Down or Binding
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The float must move freely and drop when there’s no fuel.
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If the float is upside down or installed so it hits the bowl wall or top, it can hold the needle shut all the time.
Wrong Needle/Seat Combo
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If it’s the wrong size, the needle may never unseat — so no fuel gets in.
Debris or Old Gasket Blocking Seat
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A tiny fiber, sealant chunk, or old gasket piece can block the passage right before the needle seat.
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Fuel line debris can lodge at the inlet.
Sealing Washer Under the Seat Missing or Doubled
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Many Holley 1940 seats use a fiber washer under the seat to set depth and seal.
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If it’s missing or doubled up, the seat can sit too low or crooked, blocking flow.
How to Pinpoint It
Here’s exactly what I’d do on the bench:
1. Take the top off.
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Remove the needle/seat assembly.
2. Blow through the inlet.
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With the seat removed, fuel (or air) should flow right into the bowl. If not — the passage is blocked before the seat.
3. Check float drop.
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Hold the top upside down, watch the float hinge freely.
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Make sure it drops far enough to pull the needle down.
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No binding, no interference.
4. Manually test needle movement.
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With the seat installed, push the float arm down and confirm the needle pulls away from the seat smoothly.
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No sticky feel.
5. Verify correct parts.
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Compare the old needle/seat to the new one — length, tip shape, thread length, washer thickness.
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Holley 1940 kits sometimes have a universal needle/seat that doesn’t fit every version exactly.
Quick Fix Test
If you see nothing obviously wrong:
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Temporarily remove the needle and seat.
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Reinstall the carb top without the needle/seat and test fuel flow — fuel should flood the bowl.
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If fuel flows freely with no needle, the issue is definitely the needle, seat, or float fitment.
Bottom Line
If fuel is reaching the carb inlet but the bowl stays dry, the needle and seat are still the blockage. It’s nearly always:
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Float binding or set wrong,
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Needle stuck,
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Wrong seat height,
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Or an upstream blockage just at the seat inlet.
Tip: Sometimes gently tapping the carb top with the handle of a screwdriver while the pump runs can jar a stuck needle loose.
