Gas Orifice screws into the end of the Gas Valve
It is a brass nozzle.......precision drilled to meter the correct amount of gas flow to match the combustion air flow
Proper air/fuel ratio is dependent on the orifice being clean/unobstructed
*a spider web can disrupt the flow
All Atwood & Dometic 35,000btu furnaces use the same size orifice (#51)
To clean...remove orifice from gas valve and soak it in alcohol then air dry
No poking anything thru it, No High Air pressure ---LP pressure is only 0.39psi (you can blow that hard by whistling)
*Gas valve is only rated for 0.5psi MAX
Since furnace is sooted up...you can blow out the heat exchanger using AIR Pressure
Also check the 'combustion' air wheel....no debris, ALL vanes intact and wheel is secured to motor shaft
*Missing vanes or loose ........insufficient air flow
https://pdxrvwholesale.com/products/...iv-tune-up-kit
Side Note: No pilot....electronic ignition via spark electrode