We just purchased this d50 out in loomis. stopped and put gas in it and drove it up the hill to camino. started having issuses with cutting out, black soot coming out of exhaust. at an idle it runs like a top. took it to a mechanic, he couldn't find anything..., thought maybe water in the fuel. Put in fuel treatment and filled the tank. seems to be somewhat better...but still having problems off and on...
seems to happen sometimes at higher rpm and if you shift up it helps. although I did come up the grade out of placerville no problems at all until I got off the freeway.

Seems to be an off and on issue. sometimes it runs great other times not.

Any ideas?

Would appreciate any help.