Thanks Biodiesel300TD for the link. I definitely want to look into that spring. Barry123400 and Forcedinduction said that the spring should be around 27 mm. in length. Is this spring adjustment a difficult job? Forcedinduction posted an official page that told the instructions for the job on one page, so wouldn't think it would be too difficult. We have some W123 shop manuals, so those will probably help.

From what I understand, to find the relief valve, you trace the fuel return line, back to the injection pump?

It seems that as long as you have a good way of measuring the spring, and you make sure that you don't adjust it past the recommended length, that this is a pretty risk-free job. I think I'll want to read that thread a bit more before I try it.

In case anyone was curious, I did check the throttle linkage, and it seems to be moving pretty much properly. There is a swiveling bracket underneath the air cleaner housing with a ball socket on each end for the throttle linkage. The rivet through the bracket seems to be a bit loose, which lets the bracket / arm thing flop a bit, but it seems that it doesn't keep the throttle linkage from moving all the way through it's travel.

If you do another oil change soon, put some Sea Foam in the oil & drive it a bit to help loosen the gunk better.

Ed

Since it is a 616 you should do the fuel supply pressure properly with a gauge. Read the thread and consider it at least. The 616 operated with sub standard fuel pressure is still at risk in my opinion over time.

Also I have pretty much decided after time that the 617 lift pump outputs increased pressure than the 616 lift pump does. A used one should be cheap at an auto wreckers and re kitting it before installation is both easy and cheap.About ten dollars. Or change the pressure spring in your 616 pump with one from a 617 turbo lift pump. Reconditioning it only if the fuel pressure gauge indicates it is needed.

The lower pressure 616 lift pump as new from the factory just might have been a contributing factor to the more serious suspected issues on the 616. Stretching the relief valve spring with no pressure refference is not that great of an ideal. You might get more pressure than you should have or no change if the rest of the fuel supply sysytem is not in good condition.

The springs where all not 27mm in length originally when new I think. Some appear to have been just 22 mm. Reconditioning/restoration of the fuel supply system using a cheap fuel pressure gauge will improve things much more than fifty percent of the time in my opinion..

Even better it is both cheap and educational to really get a grasp on exactly how the fuel supply system works and all the components interact.

A fairly steady 20 pounds running fuel supply pressure in the base of the injection pump will make a noticeable difference over a sub standard condition. This is all manageable pretty easily and cheaply as well. It only takes a little reading to understand for even a beginner to accomplish..