RE: Genesis, something strange...
Its a fairly well know fact that many maufactures reccomend you tune your engine at about 1/2 tank of fuel to get your engine tuned properly. This should be done with the engine warmed up. As the fuel level changes in the fuel tank you have fuel pressure changes thus sometimes causing the engine to lean out somewhat.
why they reccomend the 1/2 tank of point to perform the fine tuning I don't know maybe someone could better answer that question. I also know that many persons have had good luck running OS 8 glow plugs with this engine.
Its always good to start with the simple stuff first and proceed to the more complex. Checking the fuel lines is a very easy thing the 2nd thing Id check also.
Good luck