This guide covers the most common troubleshooting issues and technical specifications for the Stromberg BX series (including BXOV and BXVD) carburetors.
Stromberg BX Troubleshooting Guide
1. Acceleration Hesitation ("Flat Spots")
A "bog" or hesitation when you step on the gas is almost always related to the accelerator pump or a vacuum leak.
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Accelerator Pump Discharge: With the engine off, look down the throat and open the throttle. You should see a strong, instant stream of fuel. If it lags or is weak, the pump is likely worn or the passages are clogged.
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Leather Pump Cups: When installing a new leather pump, add a few drops of clean oil or fuel first and slightly flare out the cup by hand to ensure a good seal against the bore.
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Important Note: Do not use expander springs with leather pump cups on these models.
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Throttle Shaft Wear: Check for lateral movement in the throttle shaft. If the shaft is loose in the housing, it can cause "lost motion" where the pump doesn't activate the moment the throttle moves, leading to a hesitation.
2. Flooding and Fuel Leaks
If fuel is dripping from the air horn or leaking around the throttle shaft, the carburetor is flooding.
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Needle and Seat: Inspect the Viton tip of the needle for any rings or debris. Even a tiny speck of dirt can prevent a seal. Putting pressure on the needle will cause it to leak.
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Fuel Pressure: Stromberg carburetors are very sensitive to pressure.
Ensure your fuel pump is delivering between 2.5 and 3.5 PSI. Anything higher will overwhelm the needle and seat. -
Float Condition: Submerge the float in hot water; if bubbles appear, the float is "logged" (leaking) and must be replaced.
3. Rough Idle or Stalling
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Idle Mixture Adjustment: On most BX series models, the idle mixture screw is an air-bleed type.
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Turning the screw IN: Restricts air, making the mixture richer.
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Turning the screw OUT: Increases air, making the mixture leaner.
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Baseline Setting: Start with the screw 1 turn out from gently seated, then adjust for the highest steady vacuum or smoothest RPM.
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Vacuum Leaks: Use a spray (like carburetor cleaner) around the base gasket and throttle shaft while the engine idles. If the RPM changes, you have a leak.
