Originally Posted by iamvik

The mechanics are contradicting themselves. If they can't check the integrity of the diaphragm then how can they say that there's no problem? Also the diaphragm can most certainly be replaced. It is a rubber component and is not designed to last indefinitely. I think the service station is just trying to fob you off since investigating a carburettor problem takes time and effort.

I suggest you enquire on xbhp about good, reliable independent mechanics in TVM and go visit one of them. In my experience, most dealer mechanics are good enough only to follow the instructions in the service manual and nothing more.

The problems you have described do not seem to be caused by the air screw. The air screw only controls the mixture at idle and at close to idle speeds.