Car been running rough lately - oil breather hissing

took it out for a drive, was adjusting idle screw when i heard a hissing sound.

it was coming from the oil breather hose in the air filter box.

this is not normal.

tell me how bad this is?

was thinking all that hot oily air was doing nothing for the cars running/idling

was thinking about disconnecting the breather into a catchment tank just to see if it made a difference.

Over time as the piston rings wear it tends to breath more and fitting a catch can and blanking off the hole is a good option as it saves your air filter from getting clogged up and maked it run better too!

Personnaly though, i wouldnt have thought the breather pipe would be causing the hissing, are you sure its not just the carbs suction that your hearing? maybe there is a slight air leak?

i have the pipe off the airbox and going to the bulkhead area at the moment. just temporarily.

i can still hear hissing from the carb.

to increase the idle which way to turn the screw? it doesnt seem to do anything whichever way it goes.

the hissing probably ain't helping!

Have you blanked the hole off? 
Anticlockwise increases for both idle and mixture 

Blanked the hole off on underside of air filter box?

If so yes I have.

Thanks for info  

its worth replacing the crank case breather, when they get gunked up they can cause more pressure build up and you get the oil in the air box. they are about £12.
worth trying first plus they let the engine rev better when its not gunked up.