I have had this problem twice before and once it was the fuel filter was partially clogged and I installed a new fuel filter and it ran great. The other time it was the fuel line itself had cracks in it because it was so old. I replace the fuel line and it took care of the problem. Just two more things for you to check. These problems were both with a riding mower so I not sure if they apply to a push mower. Good luck. Wes