The recommended routine for a standby set is monthly operation and running it up to full operational temps each time... this should guarantee readiness and will most likely show up any defect long before you find yourself in a crisis situation with a non-starting machine. Knowing your maintenance history, keeping track of all service for a long time period will also help with accurate diagnosis. The S series has an unfortunate history with internal fuel leakage and diagnosis can be fairly painstaking for this symptom.
All fuel connections can be suspect, and especially the fuel pumps themselves. We keep a close watch on lube oil levels for any ST model we run or maintain for this reason. Any rise in level indicates an immediate need for tracking down the leak. In your case, a minor leak can also allow air into the system and thus result in an inoperable injector until the air is purged. I have a Lister training video that spends a lot of time with focus on this exact issue. These machines demand absolutely clean fuel at all times, and Lister also recommends an absolutely clean environment for any servicing of the fuel system. A very small glitch in the injector nozzle (stuck partially open for instance) can be the culprit for your described malfunction. I routinely run a dose of fuel system cleaner through mine - (100% biodiesel) will work wonders in many cases of a dirty fuel system. There are many commercial products designed for this purpose. We also insist on pre-filtering any fuel run in one of these engine mounted tanks because their on-board particulate filter is not adequate to handle more than a very minor amount of water or debris. Keep your tanks full, keep your fuel fresh. Diesel does not store well, especially if the environment is humid. This can mean a bit of a hassle if you do not run your equipment very much... but it also can reduce fuel system problems to a minimum.
dieselgman
