If the snorkel is so restrictive as to lose power, it'll do it for any fuel.
It will most likely require the LPG setting up properly again. 'Properly' in my book means on an exhaust analyser, if its not a lambda-controlled system. Once its set up right, it will work as before.
If the snorkel has one of those silly 'scoop' tops, turn it round so that its not scooping anything. That would cause mixer type LPG systems to stall on the overrun, the last thing you need is any added ram-air effect. The added benefit is not getting rain, dust, debris down its throat. They are the most useless idea.
cheers, Ross K