Bill I think you’ll find this is very common 394 problem. The issue being that they simply DO NOT WORK. This is why the 494 was produced shortly thereafter.
I tried 20 volts from a KW. Tried balancing all rotating parts out to several decimal places on a digital scale. Tried a myriad of top vent positions. All to no avail.
If you do a search on the subject, you’ll find others have rigged small fans nearby to create an airflow, but even this has its limitations.
I toiled with my 394 for months, nothing worked... eventually, and thankfully, my LHS had a lightly used MTH copy 494 very cheap. It was a revelation. It turns at an exacting 8-10 rpm at 11v, which is dead on prototypical, and has needed no attention whatsoever. Because of this, and far as I know, there have been no O scale aviators that were unable to find my airport in darkness or fog.
If it helps, the red 394 base makes a lovely platform for a water tower...
Tom