Most probably a fuel flow issue. The Rack Damper Pin allows for consistent fuel flow at idle - probably the simplest adjustment to start with, but it really sounds more like crud in the fuel system. Algae is a bad prob with these barges. Poor fuel quality often means water. Water spawns the dreaded algae, balh, blah - yadda,yadda... crud in the system. Somtimes serious dose of the right additive can do the trick. Most likely you need to clean out tank, including screen, lines and install new filters.