Not starting, Injector Spray pattern

[phorvati]

Perkins 4-108 not starting. When testing the injector spray pattern I am noticing that they do not spray every time. Its rather sporadic. Is that normal? This engine has been sitting for 10 years. I just finished re-building the block, head, valves and injector pump. Trying to start it for the first time.

Low pressure side of Injection pump has been primed. I have no bubbles at lower or upper bleeding ports. Without the injectors, i get a squirt of fuel from the high pressure lines every revolution in correct firing order i think its 1342.
When i put the injectors and orient them sideways so i can observe the spray pattern, it seems it takes 4-5 seconds before i get the first spray and its not consistent. Sometimes only 2 out of 4 shoot a spray, sometimes none. Seems like there is a pause and a revolution or two when they don't spray at all. The pattern itself is excellent. No dribbling or dripping at all.
Could it be that cranking rpms are too low to build consistent pressure?
At first I didn't get any spray at all. In fact even when i took out the injector springs, they were still not shooting any spray or liquid fuel.
I had to clean the injector nozzles as the needles were completely seized. Now they are free, i.e they can be moved by hand within the needle body, and I get them all to spray but not consistently. Should i just get a bigger battery and keep trying to start it, or is there something else to troubleshoot?

 

[banjodunn]

G'day I would be taking the pump and inj into a shop and getting them to test. Inj pumps and inj run on very fine tolerances it is poss that they are not right


Jon

 

[phorvati]

I have sent them out for testing.
meanwhile it might be helpfull for others to share what i've found out.

High pressure lines need to be properly tightened, and not overtorqued. Any leask there and injectors will not spray. They also need to be primed. Few seconds of engine cranking with nuts loosened at the injector until fueld squirts out of each connection.

Injector setting pressure can be adjusted via a screw where the leakoff line is. For pintle type injection nozzle, it looks to be about 1500psi per turn once the adjusting screw makes contact with the spring.
Since I didn't have any spray pattern, i have loosened the spring tension by turning the screw (mine was an allen wrench but some can be flathead screwdriver) CCW until there was no more tension on the spring. Then about half -a-turn CW direction.
This resulted in consistent spray pattern but very dribbly. Poor atomization. Then i turned them a total of about 1-1/2 turn CW for about 1500 PSI. This showed good atomization and no dribble at cranking speeds. I believe 100-200RPMs.

After bleeding yet again, the engine started. But it would not idle, it was running very rough and with a lot of black smoke. Too rich. So it seems i need to really test the injectors for leakage, and set the correct pop pressure. Therefore sending them to the shop.

 

[banjodunn]

G'day yes youwill need to take the injto get tested and set now inj press for them is going to be in the region of 2250-2500 psi and as you found out bleeding to the inj is needed with most perkins some engines will let you get away with only bleeding to the pump but not many


Jon