This is likely to be a fuel starvation problem.
Fuel is fed from a reservoir called the float bowl. This works pretty much like a toilet cistern with a float to cut off flow once it fills. Once the bowl empties and doesn't refill due to a blockage, the engine will cut out.
Clamp off the fuel line or turn off the fuel tap. Remove the bowl, unclamp the line or turn on the tap, and check fuel flows freely. If it doesn't, there is a blockage in the fuel line which you need to trace.
Another scenario is that the main fuel jet is blocked or semi-blocked. This can cause the engine to run ok when idling (since the idle jet is ok and not much fuel is required), but cut out as you throttle up. This is because more air is sucked in, but not enough fuel is drawn from the main jet due to the blockage. So the mixture is to weak and the engine stalls. The jet can be cleaned with compressed air or ideally a carburetor cleaning aerosol.
See my comprehensive guide for getting stubborn lawn mower or other small engines to start:
http://hubpages.com/hub/Why-Wont-That-Lawnmower-Start
Check your spark plug for debris and proper gap setting
thanks mate for the advice . John
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Thanks Mate for your time & advice . John
Just figured that 20-25 minutes run time is a bit much for a fuel starvation issue. I have seen dozens of small engines run fine until a speck of carbon or other debris crosses the spark gap shorting out the ignition cycle. While our friend Eugbug has some valid points, Orcam's razor says check the most likely cause.... dead spark.
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