[SimonIG10]

I cant fathom out the problem on my rotary mower with a 3.5hp motor fitted. It runs lovely with a new diaphragm for a few weeks then goes back to lumpy again and the only fix seems to be to fit another diaphragm. i am on the 3rd this year. I think I have bought genuine ones as came in right packaging but have now bought 5 Chinese ones to see how they compare. Again, its running fine but not sure for how long.
Any ideas? The diaphragms don't look damaged when I take them out.  The spring is in place.

[anchorman]

A friend of mine repairs these mowers etc for a living. He tells me the carb diaphrams go baggy. Mine lasted 16 yrs before it needed replacing. I used a genuine part, cost me about 8 quid! But stopped the hunting and cutting out. Then....it started playing up this year. After much faffing and tinkering it was down to a low, almost empty oil sump. I hadnt checked it for years. Filled it with fresh oil and it ran as sweet as a nut. Back to the obvious basics. Apparently, the B and S engines will play up if starved of oil as they will run too hot and upset the carburettor.  Obvious really....I suppose.