HELP!! Factory "CLICK" setting for fuel injection pump

[jhpcat]

1969 280SL:  I just got my engine back after a total rebuild by Noel in Winter Park FL.  Runs very rough, seemingly lean.  Two things have my attention.  The FIP has one click remaining on it to go CW before it is at edge.  I would think factory setting is more in the middle.  If there are 50 some click positions, then wouldnt 25 be more like a factory setting?  And correct me if Im wrong, but CCW makes it lean, right?  The second thing that bugs me is that the idle air screw (the large pan head slotted adjustment screw) can be turned all the way in and it has little to no effect on engine idle.  Uh oh... now what?  

[Jonny B]

Counter clockwise as you would be looking at the screw from the back of the pump, leans out the idle mixture.

The air screw issue may be indicating another air leak somewhere. A common spot is from the brake booster.

I will let others weigh in on the "factory setting".

[ctaylor738]

Most likely the throttle plate is not closing all the way at idle and air is getting in that way.  You need to do a quick linkage tour, or at least an adjustment so that the plate is closed and the pump is at the stop at idle.

[jhpcat]

Yes.  I agree with the lingage tour, but would sure like to think I had the FIP set at or near a setting that would be considered "factory".  Once I get this set, then the linkage tour would be next step.  Also, I will certainly look for booster leak and that I have a "closed postiion" at the throttle plate.  But we did cehck that once already.  This is so mind boggling.  You come up with anything else, I would be most grateful. 

[Cees Klumper]

I guess besides what's been mentioned, there is also the question of whether the injection pump is installed correctly or not. I would agree with you that the idle screw should probably not be where it is now, ideally, but it seems like it's been moved there to compensate for another problem. I'm not an expert on the FI pump but you have your barometric pressure compensator and the warm running device which can be shimmed too much/little, causing an overly lean or rich condition that the idle mixture screw then has to compensate for. Noel's in Winter Park best I know has a good reputation and, if the compression is what it should be, and the cam is installed properly timingwise, the engine itself should be fine. I would also check out the ignition settings - try loosening the ditributor and moving it slighty by hand with the engine running, to see if that smoothens it out. And try fresh plugs, check condenser, that whole circuit. And check fuel feed and pressure (if they haven't been for a while, now might be a good time to replace the fuel filters throughout). Good luck, once sorted, these engines usually stay tuned well for long periods of time.

[Benz Dr.]

I see this problem on quite a few cars. If you can turn the idle air screw all the way in, extra air is getting somewhere. Almost all of these cases end up being a bad IP thermostat.

 Unless the engine was run on a test stand, there's no way to know that this part is defective until the engine is installed. If the pump was rebuilt, and it should be during an engine rebuild, then this would be caught during calibration.
In some cases the throttle valve will be opened up to compensate for the defective IP thermostat which throws the linkage way out of adjustment. Closing the throttle valve will cause the engine to stall or run very rich at idle.

In my own expirience, I rarely find a massive vauum leak and it's even more rare I find a defective brake booster. All of these things are possible though so don't count them out.

[santropezblueSL]

sometimes a crack in the hose heading to the brake booster can be a air sneaky leak....

[glenn]

Hi, Start by eliminating air sources on warm engine.  1, WRD.  Plug hose line to intake manifold. 2, Brake booster.  Plug hose line to manifold.  3, Venturi butterfly.  Make sure butterfly is fully closed on stop without binding.  4, Idle air screw   Barely off bottom at turn or so.   Now, the only air getting to engine is thru the 'idle air' screw. -  Unless there are leaks--manifold gasket, cracks, WRD metal tube fitting at CSV, etc.   Now if the only source of air is the 'idle air' screw, any turning of the 'idle air' screw should result in rpm change.
       A way to monitor FIP motion is to put a 5 mm screw in the rack.  The sequence of operation--1, Start - rack moves to Full extension. 2,  Release Start (to Run)  - rack retracts to cold idle. 3,  Coolant heats up - rack retracts to warm idle as the WRD reacts.  At warm idle the FIP is pumping at minimum to maintain 750/800 rpm with no cold coolant compensating enrichment and the 'idle air' screw is adjusted to max rpm.

This all assumes timing, valves, cam, barometric comp, etc are OK.

[jhpcat]

Well... as it turns out, Hans (H&R Fuel Injection in NY) rebuilt the FIP.  Noel sends his FIP's to Hans and has done so for decades.  Hans had us turn the interior screw a few clicks (the screw inside the FIP) and now she runs like a top.  Only thing left to do is get the shifing smooth since it is very rough when you accelerate fast it does shipt hard.  City driving/ city shifting is pretty sweet.  gotta figure out how to smooth out the heavy throttle shifting though.  BTW... the car was running very lean and thats why the idle air screw made little to no difference by turning it all the way in.  Now that we richened the fuel supply across the board by turning the interior fuel screw, the idel air screw is as sensitive as it should be.  Hans said that the seeting on the back of the FIP where he had it one click frme the edge of full RICH flow, was precise for my pump baed on his full calibration and said not to worry about it one bit.  sure enough he waw right.  He is the Godfather of MB FIP's after all at about 90 yrs young.  Thank you to all of you who have chipped in to help me.  I am a perfectionist and right now, she is coming along pretty good.  but still about 2 years away from being completely restored. 

[tel76]

Can you give us a more info: on the location and  which screw you turned.