4k hours is around the time a build up can occur in the inlet manifold. Eddy also has a point about the valve lifters, they do stick on the 4Y particularily if the engine oil is not changed to shedule, Lots of guys that don't know LPG engines just look at the oil color and say the oil is OK even if it is past its service time. Have you tried a compression test?..... hope that helps Scrid
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