here is one of my videos you can listen to compare
235
...video... my idle is set at 450rpm
I took that video just after adjusting the valve.
the mailman walked up and asked whats wrong with my engine,
I told him they just sound like that.
Set them to the book with the engine warm and you should be fine.
I think the 235 calls for .016 to .018(depending on year)
...click... 
