I have a d4 6u which has become hard to start after sitting for a couple of months I think it may have a problem with keeping fuel pressure if I could receive some guidance.
Thanks in advance.

if the pilot is hard to start its bad fuel and/or carby shaft wear. make new bushes for shafts or replace new carbs are available from dealer. we let ours run dry of fuel in the carb after starting stops the fuel attacking the carb. a bit of fresh fuel each day we wanted to start it. also remember to clear the cylinders or built up oil and shit the taps are closed when handle is in line with body of tap. fuel stabiliser may help keep the fuel better avoid ethanol blended fuel. open fuel tap all the way it takes a bit for fuel to fill carb loosening the fuel cap helps.

have you ran the pilot on its own long enough to heat the intake manifold till its warm/hot to touch remember it acts as a glow plug.
have you wound the main over enough while decompressed to get oil and fuel up about 90 seconds is all it should take to have oil and fuel wait for oil before opening fuel rack
are you opening the fuel rack completely. there is a notch for full throttle, full fuel for starting is further on. we didn't know until a old bloke clued us in to that titbit. as soon as it has fuel drop the de-compressor it should fire almost immediately. turn fuel off to pilot let it run dry.

if your doing this stuff and it is still hard to start then you have
1. air getting in some where bleed the system and check for leaks make sure bleeder valve is shut the pilot makes bleeding easy you need a specially shaped spanner to open the bleed nipple on injectors hard to get this spanner guard it well.
2. the fuel is draining back out of the pump it shouldnt they are gravity fed to the filter body
3.a airlock
4. sumwan that chinese bloke turned off the fuel tap on the diesel tank creating said airlock. (i learned that lesson with old stationary engines 20 minutes taking turns to wind that crank handle till it bled through)

Thank you for your response trainzkidd88 I will look around a bit further and bleed the system it seems like it has drained back but as you said it is gravity fed it hasn't been run out of fuel, may have to check filter.

Hi Mitch,
suggest looking at the fuel flow rate from the tank to the Fuel Transfer Pump--disconnect the fuel line at the two bolt adapter on the side of the Transf. Pump and check for full line flow.
Next remove the two bolt adapter being careful not to loose the fuel pressure bypass valve plunger, spring and stop. Check for crud between the plunger and Transf. Pump housing.
Check the ridge sealing face on the old black plastic style plunger (as shown in scan) for erosion or pitting from embedded rust etc. or in the rubber facing of the newer style plungers.
As there is no pre-filter from the tank any crud from the fuel tank can accumulate here--hence the lettering "Buy Clean Fuel And Keep It Clean" on the fuel tank cap.
Give the spring a bit of a stretch and reassemble and see what you have.

As others have said if the fuel level in the fuel tank gets below the level of the filter tower bleeder screws then it is possible that with air leaks here to allow air to enter the filter tower.
If air gets pumped into the main injection pumps it can make starting difficult.
There are bleed screws at the rear of each injection pump housing on earlier engines that need to be opened one at a time from the no 4 pump forwards until air free fuel issues--then one at a time, with the diesel turning with the governor lever at full fuel, crack and bleed the injection lines at those injectors that are easy to reach until air free fuel issues tighten the lines and try to start it.
If the injection pumps do not have the little two flat bleed screws then simply bleed at the injectors.

Hope this helps.
Cheers,
Eddie B.