Kenmore Sewing Machine Table

How do I adjust the speed on my old sewing machine?
I have this crazy old retro Kenmore sewing machine (definitely a few decades) and it has a bunch of strange thumb levers and knobs, and the pedal isn’t pressure sensitive. The model number is 1120 and it’s set into a little machine table. Can anybody help me out here?
It has been serviced within the last year. It runs perfectly, I just can’t control the speed. It isn’t uncontrollably fast, I would just like the convenience. The model number is 158.510.
EDITED TO ADD: sounds like you’ve got a bad controller, then. FWIW, the 158.xxxx machines were manufactured by Maruzen/Jaguar, a good Japanese firm.
Sears claims no parts available for that machine, so I’d probably send you to Ron Anderson at A1 Syewing if you don’t have a good shop locally.
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Sounds like it’s due for a trip to the sewing machine doc and/or a new pedal. When’s the last time it’s had a professional COA (clean-oil-adjust)? The insides may be gunked up with old oil and lint, so it won’t sew unless you provide full power, or the controller in the foot pedal may be damaged.