I have a NL, but haven't had this problem. Is it possible the brushes are worn- also possibly a worn commutator? Tripping the breaker indicates excess resistance/ raising the amperage. Just a guess. Good luck.
1983 Present 42 Sundeck
Twin Lehman 135's
Steve Point Cadet/ Biloxi, Mississippi USA
*Present 42 twin 135 Lehmans