This is most often a timing issue. First, make sure your needle is in correctly, as if the hole is slightly offset, it in effect advances or retards the timing. Since many long-arms use a round shank needle, you can rotate it slightly to if needed, because sometimes you may need to do that depending on thread and fabric being used.
I don't recall which way to move it though, and don't have my documentation where I can get at it easily.