Opposed twin smoke coming out pcv and carb

My Briggs 18hp opposed twin was running fine yesterday and when I went to start it today it doesn't want to start. when it does finally start white smoke starts coming out the pcv valves and the carb.Also it dies after probably 30 seconds, any idea what would cause this?

You should check for signs of gas in the oil.  There are a couple of common reasons why gas could overflow the bowl and end up in your crankcase (e.g. crumbling fuel lines, worn inlet needle or seat, a failed shut off solenoid, nonuse of the manual shut off).  The result is an overly full crankcase (gas/oil) which seeps into the combustion chamber.
If you smell gas on the dipstick and/or the oil is above the high mark, it needs to be corrected right away...by changing the oil , checking for and clearing debris in the bowl and installing a fuel shut off valve if you don't have one.

I thought about this some more...you probably don't have a float style carb on that engine so that might not be your problem.
It doesn't explain all the symptoms, but I wonder if both your head gaskets are still intact. Keep us posted.

Well I cleaned carb, new spark plugs, new oil and the smoke is still happening. But it ran fine for about 5 mins then is back to the starting then dies. The head gaskets are intact I think because compression hasn't dropped at all. Not really sure what its deal is never had this many issues out of a opposed.

I don't think head gaskets would cause the smoke, and if you had a bad gasket, it probably wouldn't start and run like that. Is there a lot of oil in the pcv breather tube or something? What's the spark plugs look like? Wet? To get the billowing white smoke, must be either way too much fuel or oil getting in somehow. Does it look wet if you look down into the carb with the choke and throttle open before you try to start it? Don't forget pics if you find something neat to look at!

Also, what do you have to do to get it started? Do you have to choke it?

I think the smoke coming out is just the pcv is bad but I don't have it hook to the intake at the moment anyway.To get it to start I have to mess with the choke a bit to get it started but can turn the choke off after its running. Also when I was messing with it today it started doing something weird were it sounded like it would start on one cylinder then the other wouldn't start firing till a couple seconds later.

Maybe your losing spark on one cylinder intermittently. Might get some smoke when it finally picks up, but probably not real heavy thick smoke. Hard to tell without seeing it. That wouldn't explain smoke coming from the breather. Is the engine really worn out or did you get it overheated and stick the rings on one cylinder or something like that? Stuck rings probably unlikely unless you seized it up before. Kind of strange.