If all you did was change out an old, crummy fuel line with a fresh one the first thing I think of is that a piece debris got loose and into one or more of your carbs, perhaps in the fuel inlet valve or a jet. You did replace the fuel filter, too, right?
How bad was the old fuel hose? My guess other than the above would be that it was so bad it was sucking in air with the fuel, through cracks in it. If so, now you need to re-synchronize the carbs and re-set the pilot screws (air/fuel mix) as you now have CORRECT fuel being delivered.
Another possibility? While working on it you created a vacuum leak in the intake system. I've done it plenty of times.
