Nope, works just fine, at least with my 4 stroke Hua Cheng running. May be different with a HT?
I'll let you know how it works out in the wet as it rains alot here also.
That SIR light is a joke for $99. It is nothing more than some LED's in a plastic housing, about $10 worth of parts tops. This is a better deal for $10 more:
http://www.rockthebike.com/lights/downlowglow Although you can make your own with some cold cathode tubes and some ingenuity for way less.