Dave,
We have a parts list and manuals area in the Questions on lawnmowers section that has a workshop manual in it on the carby. :Wavey:
My suggestion is to remove the large washer on the poppet valve under the plastic cover and also check that the valve is set on 'C' where the cut out is in the carby (under the valve seat). You will also need to make sure that the diaphragm has not sucked in on the carby.
The workshop manual has pictures showing the position.

Also another thing that I would check is the bearings by holding the blade plate and trying to move it from side to side because if it does you will need new bearings.
