I was the lucky one who didn't have to change the engine
Same as me thought it was a fuel problem but turned out I just had to change the riser pipe and grind flat the manifold for a good leak free fit. Once you are aware of the change in running its pretty easey to pick up on. It took about three attempts to stop the gasket leaking hense me having to grind it flat. Should really have changed both manifold and riser tube in one but was a bit skint after fitting PP , sarter motor, alternator, boat cover and fitting monster racks and mirror last year.
Good luck with it