My BX 1870 will sputter and die during use. Crank it for a while with throttle open and it will start, sputter, spit black smoke, and eventually run fine again. Sometimes will have this problem when starting (whether cold or got engine). I've replaced fuel filter at engine and replaced filter under the tank with a filter/water separator. Sometimes it will run for hours with no problem, today it quit four times over a couple hours. Kinda hard to troubleshoot with it being so intermittent.