I just got a brand new serger, its the Singer Ultralock.

I just tried out serging 2 layers of flannel, and the stiching looks too loose, I have the tension set to what its supposed to be for lightweight fabric - I had it at medium weight but that was about the same... it doesnt adust any tighter so how do I fix it?

Check to make sure that the threads are going through the tension disks and not laying on the outside of the disks. Also check all thread routes. The threads must go through each and every guide. Is it all the threads or only a certain one?

Can you adjust the knife? Maybe it needs to be over a bit?