I've never tried to run such a large diameter prop, I could take a look, but something in the back of my head tells me a 16" will hit the cav plate on an alpha drive. For a 140 Merc, I'd shoot for a diameter around 14.25" and a 21 pitch if the engine runs fair. In the end it's a bit of trial and error, find a dealer who will let you test props. Been my opinion when testing to change one variable at a time. Same manufacturer, same diameter, and model, but vary pitch for instance. Trying a 21 pitch laser 2, then a 23 vengeance, then a 4 blade trophy in 20 pitch can leave ya confused. Kinda like what are the best tires for my car. To specifically answer your question, I'd get rid of that prop, but I might try it first anyway.