I echo steamraiser2’s advice, had fitted their spring and cam, ensured free and lubricated movement of the governing gear, but I state again, that it wasn’t until I had the injectors serviced and the pump calibrated I achieved a smooth and beautifully running JP3. I should also state that I fully overhauled the engine prior to that which included crank regrind, remetalled shells, new liners, piston rings etc.
I compare the servicing of the injectors and fuel pump to that of any old vehicle engine that uses spark plugs and contacts, replace with new and your engine is more likely to thank you for it.