I'm not sure from your description but I have one of these (found mine
in the alley) i think mine is model #51567 but a little hard to read.
Mine wouldn't run until I realised that it had an interlock device that
wouldn't allow it to run unless the vac tube was locked into the
bayonet mount at the impeller input or (and I'm missing this part ) a
protective screen that locks into the same place when it's used as a
blower.
Richard