Sorry if I'm telling you to suck eggs, but have you tryed timing it. Put No. 1 cylinder to TDC. loosen pump adjuster bolt then whilst pumping hand primer pump turn till you get desel out of No. 1 fule inlet pipe. Then turn back till fuel stops, and re-tighten bolt. Also there is a little adjuster on the side of the pump away from the engin. It should have a wire seal through it if no one has already played. Break seal and use screwdriver and spaner to wind this screw out (I think, it's been a while) till you get black smoke at full revs.