I just bought a 77 chevy motorhome with a 454 in

If this has a 4bbl AC rochestor quadrajet carb make sure the secondary butterfly plates completely closed after you kicked them in,

almost sounds more in the carburator. if this motorhome sat for a long period of time, when you opened it up, it increased the fuel flow in the bowl of the carb, therefor may have stirred up dirt and varnish. id check there first. if it has a holley on it, if it "coughed" or backfired through the carb when you "opened" it up, it more then likely blew the power valve out