On the 200tdi engine forum I asked about a loss of power at medium revs, loke a rev limiter but with blue smoke. I'm putting the answer here as it might apply to more engines.

I rebuilt a 200 engine from the ground up, and was chuffed that it started straight away and ran well, but when it reached medium revs the power dropped off a cliff. I checked all the usual things (fuel air lock, collapsing pipes to turbo etc) but all appeared well.

Eventually I took it into Mansfields at Bury St. Edmunds (no connection, but IMHO a great garage), dreading that they would point out an obvious problem and leave me looking like a pillock. They eventually found the problem. I had fitted new banjo unions to the new injector pump, but had not picked up that there is a restrictor in the union from the fuel return. This provided back pressure and enables the pump to deliver enough fuel at the higher power requirements. Restrictor fitted, and now drives the way I hoped it would.

Thanks to all who gave help and advice during the rebuild, piccys of the shiny newish engine enclosed. Nope - upload won't work for some reason.