Sewing Machine Mystery

Some very kind relatives gave me a sewing machine this weekend.  An old Kenmore.


It's heavy as all get out and clearly all metal so I suspect that it's a workhorse.  But I'm stumped.  It's got a big 4 on the front (as you can see) so I thought that might be the model. But nope.

Kenmore detail

It's in the 158 series, but somehow seems be the Kenmore missing link!  Try as I might, I can't find ANYTHING online about this specific model.  Lots about 158 10... and 158 12... but nothing about 158 11...!  Anyone know anything about this specific model?  Any help would be appreciated.

I've figured out how to thread it and wind and out in the bobbin with no problems but I'd love to find an online manual for it.  Also, it sews really slowly.  Not sure why.  I think a visit to a sewing machine doctor would fix it right up though!