Several days ago I was sewing on the Commodore clone, making a Whacky Bag to test all my adjustments. It was running just fine. Right now it's in my 'test case' that's set up with it's own cord block and controller:
Tonight I put the new slide plate in:
And installed the thread check spring on the original face plate:
That took some tweaking as the spring is more for the Singer 15s than it is the clones. But with a bit of alteration I got the tension set pretty good.
Then when I started to sew the machine acted strange. It would act like it didn't want to run, and it would take almost full pedal pressure to get the machine started, then it would try to go full speed. Totally unlike what it was doing the last time.
At the same time I was smelling a hot ozone type odor I couldn't find. And, I was getting a buzz from the machine. None of this happened the last time the last time I used it.
I traced the odor to the foot controller and when I picked it up it was pretty hot even though I hadn't been using it for very long.
So I took it apart and found the problem.
The top of the ceramic housing had been broken. I don't for sure if this was an old break or new, but when I took it apart, I found the cause of the trouble. Many of the little carbon disks inside were broken and crumbling.
So this foot controller is toast. I replaced it with a new electronic controller I'd gotten from Sew-Classic some time back. Problem solved. Machine is running properly now, no odor and no buzz.
The moral to this story is this. If your machine is acting up, and something smells while your getting a buzz job .... check the controller. It just might be the problem.