I have a brand new Colt carbine, I bought a SPOT red dot sight and a YHM flip up rear sight to co-witness, I had to crank way down on the front post sight in order to bring POI up 10 inches to zero in with the iron sights. The S.P.O.T red dot sight was zeroed in right out of the box.
I was shooting at 25 meters, any thoughts?
The flip up has no elevation but I am assuming YHM makes a very good sight.
I am going to try my carry handle sight this weekend and see how that behaves, still baffled, could it be the rifle? if so how to fix it? send it to Colt? I hear they take till next century.
Any good advice is greatly appreciated....

First, you should be sighting in your gun at 100 or 200 yards, not 25. Your bullet is still climbing at 25 yards so that probably accounts for some of the problem. Remember, your barrel and sights are about an inch or so apart (paralax) and not in the same plane. Light has a tendancy to travel straight, bullets don't.
Once you get out to the 100 or 200 yard firing line and sight your gun in using a bench rest, a clean bore, and shooting high quality ammo, then start looking for other problems.

I just learned a few things from "Paul" at YHM.
1.- The sight I am usid was manufactured for use on Bushmaster firearms.
2.- When the front sigth assembly is stamped "F" on the left side it is .040" taller than the standard
3.- the YHM 9680 is probably more compatible
4.- Once sighted in at 25 meters (CQ) the POI will be right on at 25, climb a bit at 50 and be dead on again at 100

In all I have just a few choices:
get a new rear flip up that is more compatible with the "F" front sight, chnage the front sight, or live with it as is.

Dremel or file down the front sight post. Or if you're really picky, just replace it.
Randall's right (as usual) about sighting it in. Near zero is where your bullet's trajectory intersects with your sight plane while traveling up. Far zero is when your sight plane intersects with the bullet's trajectory while the bullet is traveling down.
That's why I suggested sighting it in at 100 or 200 yards right off the bat. I personally like the 50/200 sight in, but some people just like having their gun sighted at 100 and adjust their rear sight's elevation appropriately. It's all a matter of personal choice.
What I think Paul was talking about, and I might be mistaken, was a very common way of sighting in your gun. First, you shoot your target at 25 yards, adjust your windage and elevation appropriately, move to 50, adjust windage and elevation, move to 100, adjust windage ONLY, and then move to 200, and finalize your windage and elevation. This is probably the easiest way of sighting in a gun since you're simply making increasingly finer adjustments the further out you go.
Good luck!