Jets in carb partly stop up use some seafoam in gas see if that clean out if run let set for atime then run again may soften what got block and go on into engine then run under load. If that don't work get kit for carb and clean all passages out with small wire you pull small wire out of wire brush makes good strong small wire you pull Brussels out flat nose pillars.
I got junior I went harbor freight pick up 6 hp matador engine and put on lost reverse but has not any problem to use.

just wanted to follow up with the goofiest fix ever - I just assumed that the new carb was properly adjusted, ran perfectly except when engaged, opened the main jet a quarter turn and works perfect now, dont forget the basics first I guess.