FUEL MIXTURE BASE SETTING

[cahoon485]

WONDERING IF THERE IS A "BASE" SETTING OR "INTIAL" SETTING FOR THE MIXTURE SCREW ON THE BACK OF THE INJECTION PUMP. I DO NOT HAVE ACCESS TO AN EXHAUST GAS ANALYZER AND IM JUST TRYING TO GET THE MIXTURE AS CLOSE AS POSSIBLE.

ISSUE: PRETTY SIGNIFIGANT BACKFIRE ON DECELERATION. LINKAGE IS ADJUSTED, THROTTLE STOP ADJUSTED.

THANKS

[Benz Dr.]

Fuel mixture settings should be done on a fully warmed engine so base line idle mixture should not be a significant issue unless it is really off by a large amount.

[rwmastel]

I think what he was asking (in all caps) was how to set the rack screw to a "default" or "factory" position.  A starting point to then start adjusting and troubleshooting.

[wwheeler]

Wasn’t sure if he was talking about the idle mixture screw or the full rack screw that is hidden in the pump. If you don’t know the difference between the two, don’t touch the pump. The injection system is an exceedingly complex beast. There are all kinds of screws and things to mess with that can get you so far off base, only a rebuilder can put it back close.

Which throttle stop screw are we talking about? Pictures would be good as nomenclature is often confusing. If it is the screw that stops the fuel lever on the injection pump, that’s not good. Only a rebuilder can readjust that back to where it needs to be. That should always be left alone.

Dan is correct in that you start with a hot engine at speed and get that right first. With no meter, you can look at the spark plugs to see if the engine is running rich or lean. Once you get that, you can adjust the idle mix using the split linkage test.

I doubt there is a base line for a pump that has been adjusted in the field. There are too many screws and shims that can be changed all of which affect the pumps performance.

This is all assuming timing and the spark is good.   

[Cees Klumper]

I think the original poster is asking about the idle mixture screw at the back of the pump, the one you turn in to enrich, and turn out to lean, the mixture. Pressing it inwards to engage the slotted screw with the detents (engine OFF).
For a base setting, try counting the total # of clicks, end-to-end, then setting it half way. Then use the split linkage test to determine whether the idle mixture is rich or lean and adjust from there?

[wwheeler]

Only thing is backfire upon deacceleration wouldn't changed by the idle mixture screw. That control is only at lower RPM ranges. That may get into adjusting the small screws near the governor which I wouldn't touch in my wildest dreams. The full rack screw is quite enough excitement. I would read the spark plugs and see what they say. Then adjust the BC or full rack depending on what the plugs say.

I am still curious which stop was adjusted. Pictures are worth a thousand words. 

[Pawel66]

WONDERING IF THERE IS A "BASE" SETTING OR "INTIAL" SETTING FOR THE MIXTURE SCREW ON THE BACK OF THE INJECTION PUMP. I DO NOT HAVE ACCESS TO AN EXHAUST GAS ANALYZER AND IM JUST TRYING TO GET THE MIXTURE AS CLOSE AS POSSIBLE.

ISSUE: PRETTY SIGNIFIGANT BACKFIRE ON DECELERATION. LINKAGE IS ADJUSTED, THROTTLE STOP ADJUSTED.

THANKS

I am not an expert here, but you did not mention ignition timing - are you sure it is accurate? Vacuum line connected as it should?

[cahoon485]

THIS IS THE MIXTURE SCREW IM TALKING ABOUT. AS WELL AS THE "THROTTLE STOP".

THIS CAR CAME TO ME AFTER SITTING FOR ABOUT 25 YEARS WITH NO KEYS, ETC. ITS BEEN A PROCESS. I OWN A REPAIR SHOP BUT HAVE NEVER WORKED ON A PAGODA BEFORE SO ITS BEEN A LEARNED CURVE TO SAY THE LEAST.

IF THIS MIXTURE SCREW WON'T CURE A BACKFIRE ON DECEL, I WOULD LOVE TO HEAR OTHER RECOMMENDATIONS.

I WILL DOUBLE CHECK THE TIMING. VACUUM LINES ARE GOOD. I JUST HAD THE BOOSTER REBUILT WHICH WAS BAD (HARD PEDAL, IDLE INCREASED WHEN DEPRESSED) I THOUGHT THAT WOULD POSSIBLY CLEAR UP WHAT I THOUGHT WAS A LEAN BACKFIRE. THANKS FOR ALL THE HELP.

[cahoon485]

PICTURES

[cahoon485]

PICS

[rwmastel]

I OWN A REPAIR SHOP BUT HAVE NEVER WORKED ON A PAGODA BEFORE SO ITS BEEN A LEARNED CURVE TO SAY THE LEAST.

cahoon485,

Hi.  Welcome to the forum!  Just so we have a baseline on your experience, how familiar are you with the Bosch/Mercedes mechanical fuel injection system?  You must be somewhat experienced with it based on your above posts.  If you want additional details....

There is a Linkage Tour thread:  https://www.sl113.org/forums/index.php?topic=5003.0
Better yet, in our technical manual, there is this:  https://www.sl113.org/wiki/Restricted/Linkage-tour

Thanks for the photos.  Now that we all know you are talking about the main rack enrichment screw on the back of the pump, and the intake venture stop screw on the intake manifold, everyone can give proper advice.

My advice is to set a known good baseline from which to troubleshoot.  There are SOOOO many things that can be worn, broken, out of adjustment.  Everyone can jump in here on what all can be set back to factory spec, but my list starts with:
- Using above links, ensure all the linkage is set to factory spec lengths.
- Ensure the intake venturi stop screw is set right.
- Ensure the ignition timing is right.  (Your rebuilt brake booster helps with the vacuum affect on the distributor.)
- More, anyone?

Then perform the split linkage test and report back with results.

(Maybe you can stop typing in ALL CAPS?)

[wwheeler]

I might make a suggestion - please do not reply in all caps. Makes it hard to read. Thanks.

Good on the venturi stop. Most, including my PO, mistaken that for the idle speed adjustment. It is not. It is there to adjust the Venturi butterfly inside so that it is completely closed but not binding. Idle speed is set by adjusting the spring loaded knob on the back of the pump (engine off!) and the air screw on the intake manifold. More fuel and air, higher the RPM at idle.

The picture I see on the back of the pump is the spring loaded idle mixture screw. That knob is on the large hex towards the bottom end of the pump. It only adjusts at idle and slightly higher rpms.

The full rack adjustment screw is hidden behind a screw above that. That screw should be just below and to the right of the starting solenoid. Remove the screw and then the rack screw is exposed - maybe. The starting solenoid lever may be in the way. I did a recent thread on that.

What I see missing is reading your spark plugs. Yes on all of the other things that can effect engine performance, but reading the plugs will give you a good idea what your mixture is doing at higher engine RPMs. There are tons of pics of what spark plugs should and should not look like on the web. 

[Bonnyboy]

Just to throw a "what if" out there.  For a backfire during acceleration have you checked the top of the exhaust where the two header pipes come together.  There could be a hole in the pipes that you can only see with a mirror which could give a backfire if open.   

 

[rwmastel]

I OWN A REPAIR SHOP BUT HAVE NEVER WORKED ON A PAGODA BEFORE SO ...

Guys,

With some basic Google sleuthing I found cahoon485's shop.  A nice little garage in Cape Cod area.  By the Google reviews, I have to assume that he's a very experience and competent mechanic who normally works on all domestic and import cars, typically 5 - 30 years old.  He's just new to Pagodas.

[merrill]

cahoon485

hi,
no need for the caps,

you have some good info from the replies already.

below are some tips (my reference is a 66 230 auto)

1. the rack screw is the last thing you want to mess with   its set when the pump is calibrated at the inj shop
2. the throttle body screw is discussed in the forums and i think in the linkage tour.   that screw is barely screwed into keep the throttle body open just a tad.

i'd start with making sure the base timing and dwell (if you have points) are good,  make sure the throttle body screw is set right.    (if you want i can take a picture of mine or count the number of turns )
disconnect the linkage at the injection pump at the top where the cross linkage is and then start the car.

if it runs you set the idle speed by turning the large flat head screw the is on the tube running from the engine (just behind the thermostat housing)  if you can get it to idle about 850 you are doing good.

form there the linkage tour and the link below will help

https://www.sl113.org/forums/index.php?topic=30450.msg220606#msg220606

once set up its great, getting there is another journey.

feel free to message me for pictures if my 66 is similar to the car you are working on.

Best of Luck!