Just installed a rebuilt GM 4.3 motor into this lift. When lift is started it has poor and doggy acceleration. When the accelerator is stepped down once or twice it drops to idle and will no longer respond to gas pedal until engine is turned off. It will flash 2 times on the dash for a flash code. Then if you accelerate it manually with the carb linkage only it will flash 7 time until you shut down the engine. This is a LPG unit and had the intake and fuel system installed from the old engine. Old engine was weak but did not react in this fashion beforehand. Lots of tar buildup in fuel system also. Any ideas or cures???