How can I fix my Mountfield SP 530?

It's the diaphragm! I had the same problem. Be very careful to fit the new diaphragm correctly. There is a gasket on top of the rubber diaphragm. The gasket goes against the carburetor and the rubber diphragm against the petrol tank body. It is very easy to tear the diaphragm when putting in the bolts. I am speaking from experience.

Dennis
October 2009

It is probably the diaphram in the carburettor has degraded and needs renewing. New one costs about £5.

David
June 2009

I have same problem exactly!

Malc
May 2009