Injection Pump tuning gone wrong

[Travis71280]

Well I decided I'd go work on the car today and finally get the tuning dialed in today but got the tuning all screwed up some how to the point she won't idle. The engine will die if you don't give her gas and I did the split linkage at higher rpms and its showing that the fuel mixture is about right but when I did the same test at idle, i pushed down on the fuel injection pump, she would start laboring or in other words the engine rpms would drop and rise constantly (the venturi constantly opens up then falls back to its stop then open up again). I even pushed the lever all the way down with the same result. I tried to instead open up the air side instead but the engine would instantly die. I tried adjusting the idle air screw both ways with no success and then I tried richening the idle mixture adjustment on the injection pump with also no success. What should I do? I don't even know if the mixture is too rich or lean. By the way the after revving it will backfire while the rpms drop. Some other things to note the full load adjustment has been adjusted before, the pump has never been rebuilt, and the car was running fine before I started adjusting except for the fact it was running very rich because I lengthened the fuel injection pump rod to richen the mixture so it could idle, but this caused the car to run rich at higher rpms. Thanks in advance for any help because I'm at a lost and kicking myself for messing with it. 

[Benz Dr.]

Any idle adjustments should be done with a fully warmed engine. Of course, if the car won't run or drive that's pretty hard to do but you should let it get as warm as it will go.

 Better check the warm up thermostat function. It could be stuck in the fully warmed position which will make it very lean when starting from a cold engine. Could be why you're hearing a back fire or popping sound.

Remove the auxiliary air filter as per usual to see if the thermostat is closed at full operating temps. Also check to see if it's even getting warm. I've seen a few that had the inlet or outlet lines plugged with spooje.

[jeffc280sl]

Try not to get discouraged because you have tried to adjust the idle screw.  Is there any way for you to get back to your baseline?   If so you can turn the idle adjustment knob CW and count the clicks until you reach the stop.   That way you can go back to the starting point and keep records of your changes.  I had to learn this the hard way.  I made changes in the linkage and the pump (idle, white and black screws) and then when it ran poorly I had no idea how to get back to the starting point.  Hours of trial and error finally got me there.

The idle adjustment knob is not all that complicated and I'm sure you will get it running better.

[Travis71280]

Thanks for all the reply's. I started making adjustments around 185F and stopped making adjustments when the motor started going over the 204F mark in fear of overheating the motor. The warm running device is working as I can see the idle drop from 1100 cold to 850rpms when warm prior to making adjustments. I didn't think to mark the baseline on the idle screw adjustment but will definitely do that once I get her running right. The reason I can't find baseline is because I made a full load adjustment and half the time I'm not sure if the adjustment screw is turning or not. I'll keep you all posted, currently waiting on a venturi throttle linkage rod to come in from MB. By the way, when making full load adjustments does that also change the idle mixture as well? Does the idle adjustment only change idle?

[ja17]

Hello,

Yes the full load adjustment does change all rpm ranges including the idle. The idle thumb screw only changes low rpm range (idle and up to 1700rpm)

The full load adjustment (main rack adjustment), can seem a little vague and it is difficult to adjust at times.   A simpler alternative is to remove a thin shim from under the baro campensator..

[wwheeler]

I agree with Joe about the full rack screw. I tried to adjust mine and gave up because I never knew if I was actually turning it. Very vague. If you have done it before, you might know what to expect. But the first time is tricky.

The compensator is super easy. I made shims from .003 to .005 stock and that seemed to be a good place to start. 14.5mm ID x 21mm OD is what I have for the shim diameters. That seems a little small but you can measure to be sure. Jeff had a proceedure to loosen the BC and jam a rubber hose to hold it firm. Then you can drive around to test the settings. A shim then can be installed to dulicate that position and tighten the BC. Very easy and easy to reverse. You might want to check the height of the BC stem to be sure it hasn't sprung. Jeff had some great pictures of that somewhere on here. 

[jeffc280sl]

Wallace brings up a good point about the baro shims.   I used a thin long screw driver to adjust the rack.  You need to use your finger tips to turn it so that you can feel the clicks.  They are definitly there, its just a hard place to work.