The adjustments for the early OM615 should be the same as an OM621. Adjustment is pretty simple. From my old Chilton's manual, to adjust the idle speed:
1. Make sure the idle control cable has slack.
2. With engine at normal operating temperature (warmed up), adjust idle speed with the screw at the venturi to 700-800 rpm. This is with the transmission in neutral for a manual or drive for an automatic.
To adjust the idle control cable:
1. Adjust the idle speed.
2. Turn the idle control knob to full idle (cable extended).
3. Adjust the idle control cable at the valve cover relay lever so there is a very slight amount of clearance at the cable end where it attaches to the linkage. Basically you don't want it limit the linkage movement to idle.
To adjust the control rods:
1. Remove the link from the injection pump to the relay lever on the valve cover (link #1
), the link from the relay lever to the venturi (link #2
with the curve), and the link from the venturi to the relay lever on the side of the engine block (link #3
2. Measure the length from ball center to ball center and adjust the links: Link #1
= 8.1", Link #2
= 12.1", and Link #3
3. Reinstall all links except for where link #1
attaches to the ball on the valve cover relay lever.
4. Push link #1
all the way down until it stops. This position is the idle stop which reduces idle variations, or "hunting". If it takes more than .04" of lift after it hits the stop to reattach the link, then adjust the link until it takes approximately .04" of lift to reattach.
When the engine is cold, the idle control cable will need to be turned to increase idle. After the engine warms up, it can be turned back down to full idle. Idle speed will increase the warmer the engine gets. Also, it is best to push the foot feed down before increasing the idle with the cable. It reduces the chance of damaging the idle control cable.
Also, I would adjust the idle control cable last if you are also adjusting the links.