Distributor adjustment

[Naj ✝︎]

Have you tried the idle air screw behind the main radiator thermostat?
Its the big slotted spring loaded screw. Turn cw to reduce speed.

naj

[waqas]

I am now contemplating adjusting the idle mixture progressively leaner until the idle is correct, or the car stalls due to fuel starvation.  Is there any reason I should not do this?

The idle mixture is supposed to be a bit rich (perfect mixture is achieved in the mid-range RPMs, whilst high-range is also supposed to be a little rich).

Naj is correct, the air screw at the front end of the intake manifold should be able to reduce the idle air (and RPMs), but this will further enrichen the mixture at idle. This might end up being sufficient. However, before you reduce the fuel (via the injection pump; and correspondingly lean out the mid-range), perhaps you should measure the CO at idle? There is a spec somewhere here...

[J. Huber]

A couple of probably obvious things. Its important to make sure the linkage is set so its not impeding your idle setting endeavors. Sometimes, the idle stop screw near air intake has been (incorrectly) used to adjust idle -- it essentially pushes on the linkage to add throttle. Make sure there is some space between this screw and the linkage stops.

Second, using the idle air mixture screw mentioned by Naj, you can use a vacuum gauge to establish the best idle speed to idle "sweetspot". With everything else (dwell, timing, plugs and linkage) all close, the idle should get you in the 750-900 range. Mine likes things a bit high -- when warm in gear is roughly 800. In park it raises to about 850-900.

Two helpful threads maybe my own travails here: (by the end we had it narrowed down to linkage -- and after my Dwell/Timing 101 lesson in another thread all has been very steady)

 http://www.sl113.org/forums/index.php?topic=6859.15

And also in the wiki, the ever-helpful "Basic Fuel Injection Linkage Adjustment and Idle Adjustment Procedures" under the fuel system link... everyone here should memorize this one...

[Largeowner]

thanks guys,

I inspected the linkage last night and everthing seems ok there.  The idle stop screw appears to be alright.  The butterfly valve is fully closed at idle.

 Naj, could you post a photo of the idle air screw?

Since I have leaned the idle mixture 6 clicks, perhaps reducing air flow will enrich mixture to the correct point...time to find a co2 meter.

Large

[Naj ✝︎]

thanks guys,

 Naj, could you post a photo of the idle air screw?

Large

Blacklick idle mixture test:
After getting the idle speed adjusted, disconnect the operating rod at the throttle body and open the throttle flap to see how many extra revs you get. That will tell you how rich the idle mixture is.
naj

[ja17]

Hello John L,

I was just looking at the photo of your distributor.  The cap is not quite correct. You may want to take a look at it since it is the later cap it may not be locked onto the ditributor and can move (rotate).  The early non-transistorized ignition distributor caps had a semi-circular cut out at the wire connection.  In addition these later caps did not lock onto the distributor like the early cap. No big deal and it may not cause any issues,  but I know how detailed you like to be. I can post some pics of the early an late caps if you like.

[thelews]

Hello John L,

I was just looking at the photo of your distributor.  The cap is not quite correct. You may want to take a look at it since it is the later cap it may not be locked onto the ditributor and can move (rotate).  The early non-transistorized ignition distributor caps had a semi-circular cut out at the wire connection.  In addition these later caps did not lock onto the distributor like the early cap. No big deal and it may not cause any issues,  but I know how detailed you like to be. I can post some pics of the early an late caps if you like.

There is a very slight amount of movement in the cap on the distributor body when it is locked in place and yes, it could vary the timing ever so slightly.

I would appreciate a picture of the original cap (probably dark color) and even better, the Mercedes part number for the current comparable/correct replacement.

Thanks.

[ja17]

Hello John,

I double checked both caps and installed them on the different distributors.  They both lock on ok unless the mechanical attachment  parts of the non-transistorized distributor interfere with the transistorized cap which has no cut out. You are probably OK.

Here is the information on the caps anyway and here is a photo with MB numbers  of the two. Yes one is darker however I believe a lighter colored cap with the "cut out"  for the not transistorized ignitions was or is available.



 

[thelews]

Thanks for the confirmation.

[Benz Dr.]

The 051 distributor has two functions:
mechanical - 20 degrees of agavance
vacuum - 10 degrees of advance

The mechanical starts at about 1,000 RPM ( can be more or less 100 RPM and still be within specs ) and the vacuum starts as soon as you open the throttle. The vacuum portion will be all done around 1,500 RPM while the mechanical will continue up to about 2,700 - 3,000RPM The way the springs are adjusted plays into this as the tighter they're set the later the advance starts and ends.

If you have less than the full 30 degrees the only way to get more is by adjusting the pull rod on the vacuum cell. Turning it out will give you more movement and turning it in will give you less. You have to remove the cell to do any adjustments.
The mechanical advance is NOT adjustable but the rate of advance is. The whole distributor has to come apart to do that but small adjustments can be made by bending the arms in or out that hold the springs in place. There is no easy way to fine tune a distributor without a testing machine.