I just bought a new bike and decided to build it up myself. I have rebuild numerous older bikes but never with a carbon fork. I went to install my stem on the new fork but the stem does not slide easily onto the fork and I don't want to force it. The bike is a Wilier Gran Turismo and the stem is an EA90. Any help is greatly appreciated.

Sometimes there's a bit of distortion, or the stem doesn't relax open completely even with the bolts removed. There could also be a small but or rolled edge at the stop of the steerer.

Odds are you can get it on with a bit of gentle persuasion. Or you may gently spread the stem clamp within it's spring range. One way to do this is to put a penny into the slot and put the screw in from the outside on the threaded side so tightening against the penny jacks the clamp apart. Don't get carried away, you want to do this only within the stems spring range range or a millimeter or so.

Silly question perhaps but the stem and steerer are the same size right? You aren't trying to install a 1" stem on a 1-1/8" steerer?

@FB, thank you for the idea I will be trying that once I get home.
@HillRider, yes the stem and steerer are the same size, both 1 1/8".

The only other idea I had was to take some 400 grit sandpaper and sand the paint from the inside of the stem.

Sand the inside edges of the stem clamp to bevel them slightly and do the same with the outside edge of the top of the steerer column. That should provide a shallow funnel to allow the parts to slip together more easily. Gently wedging the clamp open as FB suggested should help a lot.

carbon makes a torque wrench a real necessity, particularly a Noob
who has little experience in how tight small bolts can, or need to, be.

you want to avoid stripping and crushing light weight parts.

Thank you all for the help, I got the stem installed and using my torque wrench have checked that all bolts are at the correct torque.
I did have to use a combination of wedging the stem open and sanding a slight bevel onto the stem.