Onan generator Carb cleaning, no need to replace carb.

Here is my experience. Last year, due to various stuff beyond my control, I left gas in my generator, and it got fouled. I decided to try various ways to kick-start it, including a special engine start additive used with a gallon of gas, and B-12, and even though I'm not sure what specific product worked, the generator now is back to starting easily, and putting Star-Tron in it keeps it starting without problems.

SeaFoam hasn't done much for me, in my experience, so I'd say one's milage will vary with it.