Can't start 3.75 hpTecumseh push mower?

I have not used this mower for several years. I changed the plug, oil, gas and rope pulling assembly. After primming the engine, and several pulls it will start and run for 2-3 seconds. After primming again and many pulls on the rope, it may run another 2-3 seconds. Any suggestions? This mower used to start with 1-2 pulls at the beginning of the mowing season and keep running.