Fordson -low on power?

If you suspect fuel starvation, starting with the easiest point, check the filter screen in the lift pump is clear and that the pump is delivering fuel correctly. The pump lever which runs on the camshaft can wear which reduces the stroke of the pump. It is possible to rebuild the worn area with weld, ground back to correct profile.
Check/replace fuel filter(s) element. Disconnect feed from tank to check that fuel flows out freely. There is, or should be a gauze filter on the tank union which can blockup. If you have by now found much silt or sludge in the other filters it's likely the tank has an accumulation of rusty looking sludge in the bottom. Mine did, and draining the tank wouldn't clear it properly, I had to remove the tank to do it.
A blocked or dirty air cleaner will restrict air supply, as can collapsed air hoses. This will usually result in black exhaust smoke. I am assuming your pump timing is correct and injectors to be ok.

Mr. Toad
September 2008