Well first off a model number would help. I googled and found a manual for a GF 10, on page 7 it shows where the air adjustment is for the gas manifold. You might try adjusting that till you get a blue flame. About the venturi size you will probably need a pin gauge to see if its the right one, google jet size for gas and you'll get all the info on what size to use for what.
A bit of searching on the net can take you to most places where you can get first hand info on what you have and some further searching can usually provide answers, it just takes some time to dig it out.
Here's the link for a GF10 manual: http://www.manualslib.com...-10.html?page=7#manual