Small Engines (Lawn Mowers, etc.): briggs choke, briggs carburetor

Question
I was given one of the older Briggs 3 1/2 hp engines with an automatic choke that won't open once the engine starts.  It is not binding, I can move it open after starting but it goes back closed.  I assume engine vacuum pulls it open directly through the throat so perhaps someone adjusted the choke spring tension improperly assuming it can be adjusted

Answer
There's probably no adjustment.  Probably the spring is broken or missing.  If you can provide the model and type numbers of the engine I can look it up to see what it has, or you can look it up on a parts list.  You can use my parts list,  http://www.grandjunctionsmallengines.com/pages/parts/viewbybrand/default.aspx if you want.  It should be on there.  Thanks, PK.