and when in use as it heats up it looses power used it to cut the grass in the back garden and buy the time i used it for 10 mins it was hardly running
Sounds like it might be a knackered engine. As the engine heats up everything expands then you start losing compression & power.
That's a fairly common engine, you should be able to get one for very little. Plenty of mowers out there with rotten decks or knackered transmissions but the engine is ok.