Replacement exhaust

Stodge

I replace the original plastic exhaust for the genny with a stainless one.  This one has a flap on the outside.  I tested the genny and it stalled out after a few minutes.  The flap was open a bit and let water out.  Just wondering, since it's just a piece of thick rubber bolted on without a hinge if it might be too restrictive.  Anybody else make a similar switch?  

Stodge

Here's a pic

Handymans342

I replaced my flap but it didnt cause any issues