The venturi is the open inlet that slides over the brass orifice. Spiders and mud daubers love that tube, especially after winter storage. The nest blocks primary air and gas. You get flashback (flame at the shutter or under the control panel), a yellow lazy fire, or a burner that will not light at the ports.
This is not a duplicate of port cleaning (grease in the holes) or regulator reset (all burners weak, still blue). Weber GS4 tubes have a factory insect screen — inspect it; do not yank it off and call it done.
Procedure
- If you already have flame at the air shutter: knob off, tank off. That fire is at the valve end. Do not keep feeding it.
- Cold. Tank disconnected. Remove the burner: rear fastener first, then slide the inlet off the orifice. Do not poke wire into the valve.
- Shine a light into the venturi. Web, mud, or a dauber nest is obvious. Factory screens on Weber GS4 sit at this end — look through, do not tear them out as a first move.
- From the inlet toward the ports, push a bottle brush. Shake debris out the inlet, not into the valve.
- If the nest is concrete-hard and will not extract, replace the tube. Drilling sideways into the venturi wrecks mixture.
- Inspect the orifice tip. Do not ream the orifice with a wire. A yellow flame after a clean venturi can still be a damaged orifice — that is a valve/orifice job, not a brush job.
- Refit the inlet fully over the brass. A gap here is flashback even with a clean nest. Pin or screw the rear.
- Lid open. Light. Flame should sit on the port row, blue, no fire at the shutter. Soap the tank coupling.
FAQ
Why do grill burners get spider webs?
The venturi is a quiet, warm tube. Seasonal storage outdoors is enough. Screens help; they still clog. This is why you look into the inlet every time a burner acts up after winter.
Is flashback the same as a grease fire?
No. Flashback is gas burning at the venturi/shutter because the tube is blocked or off the orifice. A grease fire is fat igniting in the box or cabinet.
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