Key Symptoms Recap
Hard to start (but starts eventually)
Runs fine for days
At low speeds (25–30 MPH), it stalls as if fuel starved
Quick restart after 10–15 seconds
At higher speeds (40–45 MPH), runs all day without issue
Going to WOT does not help when it's stumbling
Most Likely Causes
1. Fuel Delivery Restriction (Partially Clogged Line or Inlet Needle)
At low speeds, fuel demand is low, but fuel flow rate may also be limited by a restriction—possibly a sticky float valve, clogged inlet screen, or gunk in the needle seat.
Higher speeds can vibrate or pressurize the restriction enough to overcome it.
Since the Carter WO has a tiny float bowl, this is significant: the bowl may fill just enough to sustain high-speed operation, but not refill properly under lighter load when bowl pressure is lower.
Check/clean:
Inlet needle and seat
Fuel inlet screen (some WO carbs have a fine screen inside the inlet fitting)
Float drop and float valve operation
Fuel line fittings for internal collapse or obstructions
2. Float Set Too Low / Intermittently Binding
If the float is set too low, the bowl won’t hold enough fuel for sustained driving at low speeds where the fuel pump pulses are less frequent.
Higher engine speeds may provide more consistent pulsing from the pump or cause the float to “bounce” and refill more reliably.
Check:
Float height and drop per Carter WO specs
That the float isn't rubbing or binding on the bowl wall or hinge pin
3. Vent Obstruction in the Carburetor
The float bowl vent may be blocked, causing a vacuum lock in the bowl at lower speeds.
At higher speeds, the air movement or vibration might relieve this restriction intermittently.
Check:
Bowl vent passages
Any added air horn gaskets or seals that might be misaligned and blocking a vent hole
4. Electric Fuel Pump Issue
Possibly the electric pump isn’t keeping up with lower-speed fuel demand due to over-pressure, vapor lock, or poor pulsing.
But that’s unlikely—electric pumps usually do better at idle and cruise than high demand.
Still worth checking:
Fuel pressure (should be <3 PSI for a WO)
Make sure it’s not pushing fuel past the needle when it is working
Confirm it has a good, clean ground and isn’t heat-soaking and cutting out intermittently
5. Fuel Cap Not Venting
Simple but often missed: if your gas cap isn’t venting properly, fuel can stop flowing after a bit.
Opening the cap lets air in, and fuel flows again.
Try: Loosen or remove the cap next time it stalls and see if fuel flow resumes faster.
Unlikely Causes
Idle well jet restriction: This would mainly affect idle and transition, not sustained cruise or WOT
Ignition issues: These would typically worsen at higher speeds or under heavy load, not improve
Accelerator pump: Has no effect once you're at steady throttle
Recommended Next Steps
Inspect and clean the float needle/seat and inlet screen
Verify float height and drop
Ensure bowl vent is clear
Check fuel cap venting
Confirm fuel pump flow & pressure (<3 PSI)
