Carb problems with a "Nikki" carb on a Onan?

I have a "Nikki" Carb on a Onan 18 H.P. generator/welder, I am trying to make the Carb work, But the carb is giving me a lot of "Grief"So I am trying to look for a carb that is re-man, or new for the onan. But it seems that no one can help me out. - It is just a simple carb problem. I have had it apart 3 times, But it seems to have "P-M-S-.- - - - - - -