Upvote:0
Since you have a B1/B2 visa someone already looked into your situation and decided you have ample ties to your home country. You should have no problems at all. At the border simply tell the truth! Also, consider booking four months out a refundable one way ticket. You can cancel the moment you are in the USA but it might help to be able to show you have a flight ticket to leave.
Upvote:2
People are generally admitted into B2 status for 6 months. The immigration officer can give something shorter if he feels like it, but generally due to reasons like having already been in the U.S. too much recently, or suspicion that you plan to work in the U.S., or something like that. There is no way to "ensure" you will get a certain amount of time. At the same time, if this is your first time in the U.S., and you don't run into an unusually strict officer, you will get 6 months even if you're not planning to be there for that long.
Upvote:4
You should have little trouble getting admitted for four months, provided that you:
You should also strongly consider:
The CBP officer will not care that you want to be a tourist for four months. You already have a visa that will allow you to be a tourist for six months! What he will look for is evidence that you are not actually visiting, and will try to live here.
If your story is inconsistent (e.g. you say you want to visit the Grand Canyon but incorrectly say where in the US it is) or you don't have at least a general outline of what you will visit, you may have trouble. But it sounds like you have fairly well planned your visit already, so I wouldn't expect difficulty.