Why is needle hitting zipper foot on left side only?

Try increasing the Stich Length to 2.0 or 2.5. I always Stich my zippers in with the same Stitch Length being used with whatever is being sewn.

We need to know the brand and model of your machine? Some zipper feet slide left or right. If yours does this, then you need to adjust the zipper foot so the needle doesn't hit.

Um, not sure what presser foot you are using--there are several.

If it is the invisible zipper foot, there is a groove in the bottom of the presser foot that straddles one strip of zipper teeth which positions it close to the needle. Zipper foot #4 snaps to either side to enable the needle to be close to the zipper teeth. The Narrow Adjustable Zipper/Straight Stitch and the Non-Stick Zipper Feet are moveable left or right.

Pfaff Presser Feet

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Assuming you have the correct zipper foot attachment for your machine, you should be able to attach it like any other presser foot. On some machines, you may need to adjust the needle position to the right or left so the needle will not hit the presser foot when stitching.

set the machine to straight stitching which should keep the needle in the center position
a zipper foot is a normal foot with 1/2 missing
It it still wanders , take it in for a service

According to this manual (pg 52):

http://www.searspartsdirect.com/partsdirect/user-manuals/3116-SINGER-SEWING%20MACHINE-manual

the zipper foot position is adjustable, not the needle position.

You ought to be able to move the needle in increments from left to right. Check your manual or the Elna website for help.

Did a google image search, this looks like a newish machine so I'd assume clip on feet?

Put the foot on the pressure plate, lower the foot on and align so it clicks into place.

Couldn't get an image of the foot but many zipper feet are designed to mount either left or right side of the foot so you can sew both edges of the zip in the same direction, ie pressure foot to left of the needle for one side, and to the right of the needle for the other side of the zip, you want to stitch in the same direction to avoid creeping.

Some machines you change the change the needle position to the left or right in order to get up close to the zipper foot.

Probably a manual would assist explaining this better, if you don't have one for the machine, I'd suggest that you obtain one.

Hi. Here's how to attached the zipper foot.

To Attach the Zipper Foot
1. Loosen the large screw at the left of the presser bar and remove presser foot (You do not need to remove the screw).
2. Hook the prongs of the Zipper Foot around the presser bar from the back, and tighten the presser-bar screw.
3. If the raised edge (zipper or cording) is to the right of the needle, adjust the Zipper Foot by loosening the thumb screw at the back of the foot and sliding foot to the left of the needle. If the raised edge is to the left, slide foot to right.
4. With presser foot down, check its position by lowering needle into side notch, making sure it just clears the foot.
5. Tighten thumb screw to lock foot into position.
When raised edge is placed to right -- adjust foot to left of needle.
When raised edge is placed to left -- adjust foot to right of needle.

Here is a link to download your instruction manual for free if that helps?

Brother Sewing Machine Instruction Manuals