When I first started using my 66 I threaded it through that hole. Then I read the diagram and it said not to. that made me wonder why the hole was there if it wasn't needed. Now I know. Thanks Joe.
It's certainly more secure running through the hole. I wonder if the thread would hang down and pop loose during darning when threaded the normal way. I never tried FMQ on my 66, I loved it for piecing though.
Have you re-checked your bottom tension? My 66's adjustment screw liked to back out when I was running the machine. I would have to re-adjust it occasionally. I gave the machine away before I tried any permanent fixes.
Rodney