Throttle Linkage / constant speed solenoid ?

[BHap]

I have a 1970 US 280SL. I am trying to troubleshoot an erratic idle - the car will idle high intermittently ~ 1,000 rpm.  The next time to stop it will be fine, then not...  In an effort to eliminate suspects I adjusted the linkage per the "linkage tour".  My injector pump linkage was placing about 1/2" of "preload" on the injector pump lever.  I adjusted the length to 233mm and then adjusted the air flap to just barely stick on closure.  After that I re-attached and adjusted the rest of the linkage so that the injection pump was on it's stop and the air flap was closed.  The car would not idle until I richened the injection pump several (5 or 6) turns.  I almost have the idle at 700 rpm so a little more richening will be needed. I guess this is reasonable given the "preload" on the pump.  When I tried to adjust the constant speed solenoid for the A/C (the car is a manual trans - 4 speed), there is not enough adjustment in the plunger to reach the throttle lever.  My question is - should I lengthen (or shorten - I'll have to look at it again) the injector pump linkage (and intake flap linkage) so that the throttle lever comes close enough to the compensating switch to allow adjustment or is there another way to achieve this ?  I suppose I could try to reposition the arm on the crossover shaft, but that has not been moved as long as I've owned the car (since 22,000 miles).  Is it ok to "shift" the linkage to align the compensating lever or does this knock out the geometry of the system?  Thanks for reading this long post - your help is greatly appreciated..

[Val]

Hi

I have a 1969 280sl and have just been through the same procedure.

You will need to re-set ALL the linkages, including the lingake to the throttle pedal.

Start with the Injection Pump rod, set to 233mm
Then the Throttle body rod, set so that the throttle plate 'just' binds.
Then the rod from the central shaft to the pivot (the one that the constant speed solenoid pushes against. Adjust this so that with the solenoid 'off' (not energised) and the adjustment on the solenoid set to half way, you get a couple of thou clearance between the solenoid plate and the lever.
Then check that you can still get full throttle. If not, keep going back to the throttle pedal.

I found the 'Linkage Tour' invaulable in this.

Hope that helps

[Cees Klumper]

Bhap: if you are happy with all of the basic linkage settings and the 'reach' on the CSS is not sufficient, one very basic idea is to simply bend the bracket on which my CSS sits towards (or away from, if that is the problem) the linkages. In fact, this may have been done on your car by a PO/mechanic who mis-adjusted the linkages, then found he had to bend the bracket in order for the CSS to achieve the necessary clearance. Unorthodox but effective.

[jameshoward]

Bob,

The linkage adjustment is very much an art not a science. I had an idle problem in that my idle was up and down when warm. I had to do the linkage 3 times before I got the idle to remain constant. Note also the importance of the idle air screw at the air intake. Delicate adjustment of this makes a considerable difference at idle (ie with the air flap closed).

My advice would be not give up with the linkage tour and search for other things to tinker with until you've had a few goes at it no matter how accurate you THINK you were!

Good luck.

JH

[glennard]

Bob, First you need to know the idle is correct-minimum fuel to idle at 800 with minimum air-then air reduced to idle at 750.  Remove the rod on the FI pump. Remove the rod on the butterfly.  Make sure the butterfly is closed on the stop.  Next check for too rich or too lean.  Slowly open the butterfly.  If rpm goes above 850, too rich.  If rpm goes down, it should after rising to 800.  Then slowly open the FI pump arm.  If rpm goes up, engine lean.  If rpm goes down, it should.