Longarm machines are multi-directional giving more accurate stitching while moving the machine in any direction.
You need to use Multi-Directional Needles -- you recognise this as MR or SAN with Groz Beckert and other suppliers
With the naked eye, it is hard to tell a difference between needles. But when you are stitching at 500 or 1,500 stitches per minute, you can definitely tell when you have a good needle or a bad needle.
The designation of 'MR' is "Multi Range" (also known as SAN: Special Application Needle) which was created for the textile industry, more specifically, the 'MR' needle style was developed for automated sewing processes with multidirectional feeding systems. If your machine is not stationary (such as a Longarm machine), then the 'MR' needle style is the one to use.
#14 = MR 3.0
#16 = MR 3.5
#18 = MR 4.0
#19 = MR 4.5
#20 and #21 = MR 5.05 )
Mid Arm Machines work really well with the Correct Needles - Groz Beckett is recommended by the top Manufacturers Janome Artistic: Innova: Babylock Tiarra, Sweet Sixteen etc