At what distances are you shooting bullet holes through paper with the new carbon arrows? Or was the paper tuning done with your aluminum arrows?

The difference between a mechanical and a fixed blade is the mechanical does not wind plane as bad and flies much more like a field point. Hence more forgiving. You could shoot field points with 6 or 7% foc and do it accurately with enough fletching. I doubt you would have that much luck with a fixed blade that will catch the wind as it flies thru the air. So if you shot mechanicals you could get away with less FOC like a target type arrow and still have it be fairly forgiving. This is why many shoot them, they easier to tune. It's the wrong reason, but never the less it happens.

More FOC forces your fletchings to work harder. This helps your arrow stabilize faster and stay that way. I have never seen too much FOC make an arrow fly bad. I have seen too much tip weight lower spine and make an arrow fly bad though.

What size are your aluminums? If they are bigger than 19xx then the nocking point will not be the same from arrow to arrow because the aluminums are larger in diameter. Going to a smaller diameter arrow without changing your nocking point or adjusting your rest will lower your impact points.

Also by adding weight to the back of your arrow you could have changed the dynamic spine. Adding weight to the back stiffens your arrow.

Is this a problem you are having with a broad head on your arrow, or with field points? I am confused about that part.

A simpler answer is you can't just change arrows and not anything else and expect things to be the same. Sometimes you get lucky, but usually you need to retune your bow.

Paul

i had this same problem last fall when changing from aluminum fletched arrows at 28 inches and 125 grain thunderheads to gold tip hunters with vanes and 100 grain thunder heads all with 65 lb draw. i think because i changed broad head weight it made my arrow flight corkscrew after twenty yards. anyways, i asked the guy at the proshop and he threw my arrow with the broad heads on the straightness checker. When rotated every one of my broad heads was wobbly as hell, even the ones i had never shot. That could have been from the inserts not being glued straight/correct or from crooked broad heads. try checking the broad head alingment and adjusting as necessary, or maybe try changing to higher quality broad heads with shorter blades (not cutting hole, blade length). Also are you hunting or target shooting? If you are hitting good groups at forty yards i wouldn't worry about paper testing. Are you gonna be shooting papper or bucks? Bucks don't care if you puch perfect holes. Check that your rest is centered properly and that you nock point is still correct. Streching/wearing strings can change the nock point and travle.
good luck