I have had my bike for a little over a week now. It has carbon fiber handlebars but they need tightening. I tried to tighten them yesterday but were lose at the end of a 20 mile ride. I could take it to my LBS but the place I bought my bike from is quite far away. Has anyone had experience with tightening carbon handlebars? How tight can you get them before it starts to crack?

5nm is a typical torque spec for carbon bars.

torque wrench with the specs from the manual for the handlebars!

That's the advice you need. With so many more components being made of carbon fiber, a torque wrench is a must have, and follow the manufacturer's tightening specs.

Also, if it'sa 4 bolt stem, follow the reccomended pattern for tightening the bolts.

I think we might have one of those, but I don't have a manual for the handlebars. All I know is that they are Felt. My LBS kind of made me a bike with good parts they had lying around so I only got a manual for the frame. I was using a screwdriver with an attachment to tighten the bolts.

You'll need them quite a bit tighter than that.

Check the internet. You should find some type of indentification on the bars, then you can find probably find the manual in PDF form on the net.

https://www.parktool.com/repair/howtos/torque.pdf

I don't know about carbon stems and/or bars, but for my lightweight aluminum stems (Syntace and Ritchey WCS), the torque spec is for the stem bolts, not the handlebars. Both of my stems have the torque printed right on the stem, the handlebars do not. If I was installing carbon bars onto those stems, I would not exceed the torque specified for the stem, regardless of the maximum specified for the handlebars.

Does your stem have a torque spec printed on it? It's likely to be a number of "Nm" (newton-meters).

I do know that the torque recommended for installing my carbon seat post (bontrager) is a lot higher than the torque spec for the alloy stems, which leads me to believe the critial link is the threaded part of the stem in the handlebar-stem interface.

Again, take my comments for what they're worth. Try to find the torque spec for your handlebars AND stem. I'd look on the manufacturer's website, but I'd definitely call the shop you purchased the bike from and discuss. You don't want to overtorque any of this stuff: you can strip and ruin expensive stems, or dangerously weaken either the stem or bars.

Consider a carbon prep compound as well, if it hasn't been applied already.