Have a 1985 sumitomo s160 f2 excavator about 7.5 tons. Has a 4jb1 Isuzu motor. It's started spuddering a lot and trying to stall out. I cleaned the fuel tank, replaced the fuel line from the tank and have replaced the fuel filter numerous times. Seems like it gets worse when I get the machine rocking and bouncing alittle bit. When I stop and let it idle it will clear up but when I get working again it starts acting up. I assume a bad injector wouldn't go in and out of running good and bad but I'm not a mechanic. Any help would be appreciated. Thanks