Mary Parrish of course the presser foot should be down when serger is in operation..sorry if i did not word that correctly..however even tying on and pulling through sometimes the knot on some models will not get "into" the tension and there will be difficulties/ most models are quite easy to thread and if you use a serger even tie ons break occasionally and you should be able to thread without tying on.

If my lower looper comes unthreaded I tie the end of thread to dental floss.Then thread it. The dental floss makes it easier.

I have an old White serger that has served me very well. Yes, at first threading is difficult, but with practice, it gets better. The lower looper is the hardest for me because of the delicate threading tool used to get the thread through the part below the needles. My old machine (1987) has markers for each thread passage. All I have to do is follow the path of red triangles, circles, diamonds, and squares.

Someone mentioned getting a good stitch after threading. If I don't get a good stitch after I've threaded the serger, I cut the threads and start over. I find I save time by doing this.
Also if I need to adjust the tension knobs, I turn all of them back to zero and work my way back up again.

Open the door on the bottom there is a diagram.

I have a baby lock. You put upper and lower loopers into their perspective holes, push a lever and a miracle happens. They are threaded. Baby lock uses a puff of air to shove the thread through.

does the baby lock puff the threads all the way to the needles, so all you have to do is thread the needle?

No, it is very easy to thread the needles. The puff of air does all of the lower threading which is my understanding the hard part. The thread that goes to the needles only goes through two hooks and then the needles.

I also have one I don't use much. Someone said to break the thread, tie the thread to the new color and pull through until you get to the needle. Hope this helps.

I have a Janome, threading is easy. Although the manual says to thread in order 1, 2, 3 then 4, my thread will keep breaking. I have discovered that if I thread it 2, 1, 3 then four it works every time without the thread breaking. No more frustration, and it only takes about 5 minutes to thread. Might want to try that.

The instructions that came with my serger are also in error. That's one reason I have to take it to the shop to get it threaded! froggyintexas