i had issue on my 940t and that big pipe accross the cam was the issue, it may look big and be clear (i could run degreaser thru mine easily, but mine had coked up enough to not be breathing right...I spent an hour with a piece a plastic coated wire and degreaser (made the hose into a U shape, filled it ran the wire through it, emptied - refilled repeated) and was amazed at (a) the amount of hard rud that came out and (b) the difference it made!

just a thought - also it doesnt have a flame trap installed does it - cos i believe it shouldnt have! (i.e. fitting is there but mesh isnt!)