The founder of the '70s band Boston has more than a feeling that his ex-guitarist is ripping him off ... and that's why he's suing the guy.

Boston founder Tom Scholz says former axe-man Barry Goudreau -- a member from 1976-1979 -- is committing musical blasphemy by using the band's name to promote his solo career.

Let's go way back in time ... when Tom gave Barry a severance package to leave the band ... including 20% of the royalties for the band's first two albums. According to the lawsuit, Barry agreed to leave the Boston name alone for good.

Now Tom says Barry has been trading on the name ... even performing their songs at his shows.

But really, all Tom wants is to have his peace of mind. And lots of money.

Credit: TMZ