Whirlpoor Range # SF362LXSS0

I may be blind or stupid, but I find no air shutter or other way to adjust the air flow for the upper 4 burners. There is an air adjustment by the regulator which seems to be for the oven. Either way, it is opened full yet my one burner flame still has very yellow tips. I am told yellow flames need more air to turn blue and burn properly. With the lower shutter fully open, even if it is also for the upper burners, I cannot provide more air from that source.