Air/fuel ratio adjustment using the split linkage method?

[rgafitanu@gmail.com]

I found here a 10 year old topic posted by member Bob from Memphis about how his lean condition has been corrected by Joe Alexander at the 2007 PUB. Here is the post:
https://www.sl113.org/forums/index.php?topic=7178.msg46063#msg46063
If I understand correctly Joe fixed the lean condition by pushing on the "offset" linkages until WOT and increased the IP idle screw a few clicks at a time until the engine would not cough. By "offset" linkages I mean that the IP rod was disconnected from the connecting rod and pushed down about 1/4" and with this gap maintained, both rods were moved over the travel range. As the engine was coughing Joe would stop, increase the IP and continue until no coughing.
It appears from the post that this adjustment corrected the AFR generally and not only at idle. While it contradicts many statements in this forum that the IP screw adjusts only the idle AFR it is also confirming other statements that individual changes to the IP screw or the WRD or the barometric compensator will affect AFR at all other ranges and conditions.
The reason I am asking about this is because such a method appears to be the best so far to adjust AFR. While all other methods require a CO or AFR% gauge (with its own mounting/testing difficulties) and lengthy driving periods to allow for changes to settle this is straightforward and fast.
Adjust IP screw until engine does not cough.
To Joe and to other members, is my assumption above correct or am I missing something?

Thanks,

[wwheeler]

By IP screw, do you mean the visibly external thumbscrew that should only be adjusted when the engine is off? If so, that screw is effective only between idle and somewhere around 1200 RPM. Given wear and tear on these pumps that number is not absolute. But it doesn't effect the entire range. The full range screw inside the pump changes the full range. Then there are the other two screws on the governor that I would never try to attempt to adjust. You really have to know what you are doing with those.

The oval WRD shims in theory only change the mixture when the engine is cold and the thermo-bulb retracted upward. I say in theory because If have witnessed a very slight amount of change in the mixture when the engine is hot. Doesn't make mechanical sense, but it happened. Even then, not sure how effective it is at anything but idle to 1200 RPM.

The Baro comp is absolutely effective in changing the mixture at all ranges and at all temperatures. That I know that very well and is easy to do. 

I may be reading that 10 year old post wrong, But I think they are talking about mixture at idle speeds. I never saw any mention of WOT (wide open throttle) and not sure you would ever want to do that to an engine that is not under a load. To me, he is just describing the split linkage test.

[rgafitanu@gmail.com]

Wallace,
The thread that I refer to mentions that Joe had to do “18 clicks a couple of clicks at a time with the engine off” which leads me to believe it is the aft push thumb screw. I know that it should be only for idle. I was hoping Joe A. would clarify which screw was adjusted with this method.
The reason I am asking this is because this method appears to be fast and more accurate in determining the correct AFR. At least for me the split linkage test is very imprecise. When I thought I achieved balanced AFR, the car moves like a sick dog and after a while the plugs show lean white deposits. I don’t want to start welding bungs in the exhaust and I couldn’t find somebody with an AFR here in southern MA.

[66andBlue]

Radu,
did you follow the procedure described here?
https://www.sl113.org/wiki/Restricted/Linkage-tour#Idle

[ja17]

Most likely the engine was suffering from an extreme lean low RPM fuel mixture. Since the coughing occurs with a lean mixture, at low RPMS during initial acceleration, the low range adjustment (thumb screw) richened the mixture, at low rpms,  and cured the "lean coughing". Make sure all fuel filters and fuel screens are clear in the system. A clogged filter or screen will lower fuel pressure and volume and can also cause a "coughing" during acceleration. Yes the "thumb screw" effects fuel mixture at lower rpms and idle. The baro compensator shims and the internal rack adjustment screw can change fuel mixture on all rpm ranges at once. Fine tune each speed range with the "thumb screw" and the internal two pairs of governor screws. Make sure your engine is in good tune and your engine linkages are correct before any injection adjustments or you will be wasting your time!

[rgafitanu@gmail.com]

Alfred, I did adjust the idle speed according to the technical manual. However if your AFR is off the idle air screw in the manifold may not adjust much.
I think that I am into a (very) lean condition. I will adjust it again so that the split linkage shows rich and take it from there.
Thank you Joe for clarification.

Radu

[rgafitanu@gmail.com]

So I took the Barometric screw (replaced the BC with a screw and a lock nut) out 1/2 turn to make it richer. The car runs like it got a new life, it has power and the idle air screw now adjusts the idle. The split linkage test shows me it's rich but I will stop checking it until I get to someone with an AFR to do it right.

[wwheeler]

Yeah! The BC is a very sensitive adjustment and it doesn't take much. Somewhere here there is a post about determining if your BC is shot. It is just a simple measurement assuming you do not live in the Himalayas. That part is NLA and I have never seen one for sale. When it is shot, you have to do what you did and that is to use a screw and a lock nut. 

[rgafitanu@gmail.com]

My BC is not working very well, very little if any extension under vacuum. I replaced it with a M12 bolt and a nut, I am the sea level and I doubt I will drive Gretchen 200 miles to the Washington mountains any time soon. You are right Wallace it is very sensible, 1/2 turn was a lot, I have to turn the IP thumb screw more than 4 clicks back to bring down the idle rpm.