Absolutely it is possible. Had the same thing happen with an old Evinrude 55 HP outboard. I replaced some part or something and it would run great on the hose, but not in the river. I got really angry at the boat ramp with wife an 3 sons all ready to go out in the boat and it would spin for ever, but never fire. I pulled the trailer out of the water and cranked it up and got my wife to back the boat into the water. Once the boat got about half way in the water, it shut off and would not start. I called my "boat guy" at home on a Saturday an he told me which wire to disconnect and told me the boat would run all day, but I'd have to ground that wire in order to shut the motor off. Basically, I had connected an ignition wire to ground that should have been connected somewhere else. If you can find a wiring diagram, I'd compare it to what you have. Did your repair require taking off any wires? May have some connected incorrectly. Look for connectors unplugged.
