Here are my recommendations:
1 Re-oil it (mine requires ever 10 hr - i do it about 8)
2 Completely re-thread the machine (take off the spool and start like you had no thread on it)
3 Take out bobbin and carrier - remove bobbin and re-insert (I too when in a hurry can do this backwards)
4 Clean out lint from thread plate and bobbin area
5 New needle
Good Luck!!