[77newell]

Something is limiting the fuel being supplied by the injectors to the cylinders until either sufficient flow has occurred or some critical part has warmed sufficiently. The items that can limit injector fuel flow are: the injectors, the governor, the fuel filters, the fuel pump and the hoses between the the tank and the engine. The question is which one(s) of these would likely cause the symptoms you've seen gradually increase. I'm comfortable ruling out the injectors and the governor since I can't come up with a reason why warming up would take 15 minutes or so. The fuel pump can be ruled out by manually pumping it (if you have the hand tab that mine does) and seeing how many strokes it takes to produce resistance that indicates full pressure. It should not take more than a couple stroke - at least on mine. So that leaves the filter and the hoses. Since the filter is cheap and easy to change and others have had it work I would go with that first. If that doesn't do the job then I would be checking the hoses that are close to the engine. I would try squeezing them while cold to see of there are any soft spots that might indicate an internal collapse. The most likely candidate is the supply hose since it operates under suction. I can't figure why a restricted return line would do more than stress the fuel pump, though that may be just my ignorance speaking.

Please let us know how things progress. It is always useful for future reference to pass on what worked, especially if it is something the rest of us missed. And if it was something we suggested that feels really good too.