How to reverse on a Viking 5610, and what size needle

Try using a Schmetz stretch needle size 11 )7015-HS)

http://www.amazon.com/s/?ie=UTF8&keywords=schmetz+130+705h&tag=googhydr-20&index=aps&hvadid=31589294077&hvpos=1t1&hvexid=&hvnetw=g&hvrand=17197811914288753541&hvpone=&hvptwo=&hvqmt=b&hvdev=c&ref=pd_sl_5hzcn08ee3_b

The part is no longer available from Viking. However, you might be able to buy a used one on ebay or from sewing machine parts. However, you might try contacting some of the Viking stores to determine if they have a used one from a machine they use for parts. You can send me a private email and I'll give you some Viking dealers you can contact. email: [email protected]

try this link for parts and needles
http://www.sewingpartsonline.com/husqvarna-viking-936-sewing-machine-parts.aspx

SKIPPED STITCHES
1.the needle is not inserted correctly
2.the needle is damaged
3.the wrong size needle is being used
4.the foot is not attached correctly

You need to slow your speed and use a larger size needle - 14/90 or 100/16.

The groove on the shaft of the smaller size needle cannot properly guide the thread through the thick layers.

A dime usually will work if it is a slot. If it is a Phillips (+) size 0 may fit.

If you have to purchase a screw driver, put the screw in a baggie so it does not get lost and take it with you so you get the correct size.

A screwdriver should have come with the machine.

I'm trying to find a machine similar to yours and have done much research re: the older mech viking sewing machines 6000 series. They are GREAT machines, suffering only from problems such as yours caused by the old "lube/grease" they used when it was made @ factory. In their efforts of making a "never needs oil" mech sewing machine, the grease tends to harden & freeze up the gears & cams inside the machine. You need to have it serviced @ authorized Viking shop as you have to completely disassemble the machines & gears, clean, re-lube, & re calibrate the gears... I understand this s/b ~ $175. Money well spent considering if taken care of your beauty could be sewing for another 60 yrs!
Hope this helps!

Sounds like the motor belt has come off the machine. It needs to be serviced by an authorized husqvarna viking service technician. You can locate a dealer near you by visiting the husqvarna viking website and clicking on the Dealer link on the left-hand side of the page - http://www.husqvarnaviking.com

Good luck.

THis problem occurred as I was sewing on Neoprene. I was using Gutterman all-purpose thread and a size 80 needle. Tried switching to a size 70, then to size 90. Still unable to zig zag. After inserting a test sample of cotton, the zig zag worked perfectly, so I knew it was not a mecahnical problem. I switched needles again. This time to size 90 for stretch fabric. Voila! Problem solved.