Small Engines (Lawn Mowers, etc.): mountfield self drive lawnmower, diaphram, self drive

Question
lawnmower has briggs sprint sp470 engine and is running very rough plug black so too rich no adjustment on carb(plastic) guess thats why they are cheap.been told it needs new diaphram which is not expensive but is it difficult to fit.am reasonably competent but looks quite tricky getting carb off.

Answer
 Hello Billy:

 I Require the Numbers off the Engine to Help More, but I am Familiar with the Carb and Mower you have. The Carb can be Overhauled, however I dont Suggest for this Carb that a Homeowner try it. These Carbs can be a Real Pain to Get to Work Right. They have No Adjustments and Must be Perfect when Overhauled. Hope this Helps. Let me know what Happens, Please.

 Good Luck

 Respectfully

 John