Just reviving this thread again as I have a similar issue with a 2H (auto).
Under normal driving there is no black smoke, but when the rpms approach 3,000 I get black smoke, and as I understand it, there shouldn't be any black smoke at any rpm, except maybe in the red zone at 4,000?
I took it to a diesel specialist 3 years ago, and they determined that the fuel screw was set too high, probably by the previous owner to get a bit more power out of it. So they turned it down 2 full turns.
Black smoke at higher rpms was gone, but returned again a few months later, though I did not initially notice it, because I never go above 2,000 rpm.
My questions are:
1. Should I turn the fuel down even further?
2. Is it possible the screw wound itself back out again after the diesel guys wound it in?
3. So, the maximum speed screw doesn't just dertemine the maximum rpm, but the maximum fuel at all rpms?
4. And finally, just a confirmation after consulting the FSM, that this is the correct screw for the auto pump? (as always, things are different on the automatic transmission fuel pump)
Thanks,
Vince