hard start D4

D47J takes a long time to get going, and usually main motor is warmed up from pony working overtime! After its been running, it will kick right over after being stopped. I thought maybe it was a compression issue? What is the procedure for checking the compression? A friend thinks maybe its an injector problem? How would I conclude if they are the problem? Then what is a fix? There is a metal line that runs from all the injectors, then down and out the bottom of the tractor. This line drip fuel when running! ???
Thanks for any input, Bob

Bob , How is the fuel pressure while the pony is turning the main engine ?....this will cause hard starting when cold. the metal line is a overflow/bypass