Unit starts and runs nice. While mowing, after maybe 5 to 10 minutes, starts to misfire on cyl 1. Verified by cracking injector lines and cyl 1 is not contributing. Replaced that injector. Bled fuel system and unit starts and runs nice. Cut grass for 5 to 10 minutes and starts to misfire again. Retest and cyl 1 again. Could it be the injection pump?