i am using a nylon fuel pipe would it be okay to use 10mm copper pipe to connect to the carb
i am using a eletric fuel pump

yep, should be fine, that's what me and alot of others are using.

Rich.

Are you sure that you don't want 8mm??

I don't know your application but I know that I used 8mm microbore copper tubing, as the 5/16" fuel lines (as used on most cars) are a direct push fit over the ends of the copper. I swage a rib onto the ends of the copper pipe using a flaring tool to stop the rubber blowing off (injection lines)

Possibly your lines are bigger, perhaps 3/8", but I don't know, if so, ignore the above!