Rough running manlift
 

Good evening all..... I am using a manlift trying to complete work on our garage. The manlift has begun running very rough and will not throttle up. I have tried replacing all of the fuel lines as well as the fuel filter and have attempted to bleed all of the air from the system however I am unsure if I have accomplished that. I have cracked each of the injectors a little bit to make sure there was no air coming out and it seems to be bled pretty well. The engine will start and run at an idle but after a minute or two will begin to idle rough and will not throw up. Every time I attempt to put a demand on the engine it runs even worse until it eventually stalls. There have been a few times where I have again attempted to bleed air from the system and it seems to run for one or two minutes at a high idle and then runs rough again until the idle comes down and will eventually stall again. After each of these episodes the engine will start an idol, again it idles rough but it does start and run. There are also small lines above the top of the engine which appears to be a fuel return line that goes back to the fuel tank, there was a screw in one end of that line and I took the screw out to bleed air from the system which seem to work for a few minutes but then repeated the problem again. Since that time in an attempt to be sure that I had bled all of the air from the system I extended that line from the top of the motor into a jug to catch any diesel or air that escaped so that it would not spill onto the ground or all over the engine. It does appear there are bubbles at times coming out of that line and into the jug but I am unable to figure out where the system may be pulling air.

The lift is a 2003 Genie S40. Any help or insight would be very much appreciated.