I have a Mountfield SP544. I've had it for about five years with no trouble at all. Service it etc. Suddenly its started revving erratically, The throttle lever on the side of the engine is rocking back and forth constantly causing the revs to rise and fall. I have had the carb off and cleaned it checked the plug but it hasn't helped. Compression seems ok. Runs a bit rough and eneven on low revs. The throttle cable doesn't seem to work the throttle directly but via some kind of internal mecchanism. Can anyone help me out with suggestions as to the problem. Thanks
Hi again. Finally found the problem, not the diaphragm as suspected. The throttle cable clamp on the side of the engine had worked loose and the accelerator had got out of phase with the governor. Operators manual has a bit on resetting it.
Pete, June 2012
Yes I get it now, same as a gasket, just a different word. Thanks for being so helpful, I will try this, and check all the springs are still there too.
Pete, June 2012
Have a look here, there is also tutorials on how to replace the diaphragm. Post if you need help.
£4.96 for this one
Thanks for that advice guys. Sorry if this a silly question, but what is a diaphram kit? carb looked really basic without too many moving parts. mine has one long spring that runs the length of the throttle wire and a couple on the cable linkage from the throttle lever. wondered if any had dropped off but I have no way of telling.
Pete, June 2012
I agree, but more like £1.50.
phil_saunders(a)bigfoot.com
Phil Saunders, June 2012
You need a new Diaphragm kit, about £15.00 at a good lawnmower shop or online, easy to fix just remeber to replace the springs on the carb correctly
