Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Welcome to JUST ANSWER small engines, let me try to help you !! I don't know it all, but maybe together we can get you a satisfactory answer!
Not normal! Is the engine missfiring? With engine idling, loosen one high pressure fuel line at a time , to see if one cylinder is misfiring. Do each cylinder, same as shorting out a spark plug on gas engine. Sounds like you may have a cylinder misfiring , from bad injector nozzle or other cylinder problem. If you can isolate the cylinder, then you can check the injector nozzle , by swapping with a known good one. and you can check the valves on the misfiring cylinder.
Raw fuel from exhaust always seems to be misfiring cylinder. Do you seem to be getting more exhaust smoke? I would run cylinder test, just to know all cylinders have equal load.