help with pilot with low yellow flame

[SAG30]

yesterday I replaced the filter on my furnace, I saw that the air filter compartment was very dusty so I decided to clean it up, for precautions I unplugged the fan motor and turned the pilot off. After I was done, I plugged the fan back in and tried to light the pilot back on as well, however, the pilot will burn a blue steady flame at the beggining but then the flame get weak and yellow, can someone help me with this? your help will be appreciated. Thank you

[HayZee518]

Ablue flame with blue inner cones indicates a good air-fuel misture. When this misture is upset, the flame attributes its color to the situation. Check the venturi opening and see if there is something obstructing the air opening. Too little air would cause the flame to go yellow.

[SAG30]

where would I find the venturi opening?

Thanks for you reply, could you please tell me where would i find the venturi opening, the furnace is a Lennox G12Q3. Thank you

[HayZee518]

the pilot flame burns a low volumn of gas (propane) or natural gas. the main gas valve uses a jet partially open to the atmosphere inside the burner tube where it mixes with air for the combustion flame. sometimes when you stir up the dust inside, the fine particles of dust mix with the air and is mixed with the gas and burns with a yellow flame at the burner bib.