please help, should be easy
 

I have a 1975 F-250 and it has a very low idle. When I first start it up it is hard to get into a gear without it dieing on me. I have to gas on it while braking to shift in order for it to stay going. This only happens when I first start it but I believe it is an idling problem so the question is what is the proper idle speed for it and how can I adjust it? any info would be appreciated, thank you.