Most propane devices have an air mixture mechanism.  This is used to
regulate the amount of air drawn into the propane/air stream that feeds the
burner.  I'm not sure where it is on the westie burners but if it's
adjustable then you can add air to make the mixture burn 'blue'.

The spiders are a constant problem.  Blow out the tubes or use a pipecleaner
(remember those, Joel?) to whisk away the little critters.  Even a small
amount of web can restrict the flow sufficently to make the burners
"yellow".

pensioner