[Farmall] Farmall C carb question

[PROFARMALL at aol.com]

Hi all, 
I just changed carbs on my 1948 Farmall C  and had a few question, what 
causes a governer to  seach for a set rpm , like at wide open throttle?  and why 
does closing the choke half way make the engine run normal? It seems like it 
needs more fuel. My old carb had a main needle adjustment screw and the 
replacement carb doesnt, I was told that the old carb was a distillate carb. The main 
jet in the old carb has 27 stamped on it and replace has a 30 if that helps 
anything, Any thoughts would be appreciated. Thanks in advance Ed