<<Do we need to live with this confusion or is there any definitive explanation?
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Well, here is an attempt.....
The design of the cold start and cold run on these 113s has gone through 3 start versions and 5 or 6 pump changes ..so not all applies,
But , the general COLD RUN design is this:
When coolant temps are low , the cold start thermo on the pump senses low temps , it opens a slide that allows more air to enter the engine [ even though the throttle plate is closed] ..this is Auxilary Intake of air [ at the air filter on pump] ... at the same time , it moves the Fuel Rack foward to allow for more fuel {Enrichening the mix] This should bring the rpms UP ..As the coolant temp heats the thermo valve , it decreases the rack position and starts to cut off the auxillary air , keeping the a/f mix proportional.
When the engine temp get near normal, this apparatus is no longer needed and should have completely cut off the air entering the filter and also let the rack go back to its nuetral position...in other words , it is DONE and now has NO EFFECT on the a/f mix .. kinda like a carb cable choke that is now full open and moot..
So , in theory, the lowest RPM at idle will be after the Thermo valve is DONE with its job..any time it is in the circuit, you should have HIGHER THAN NORMAL rpms...if you DO NOT , then your pump and linkage adjustments are incorrect..[providing all ignition specs are met]
So, how do we know ??
You pop the cap in front of the pump and screw a 5mm screw into the Test Hole at the end of the rack [ unfortunately, the late pumps, after R22, no longer had this convenience] .. While the car is warming up . you watch the screw .it should be foward while warm-up
[ richening the mix] and at warm -up, it should go in..
..now , here is the trick...
..as the car is warming and we are still in the thermo operating warm up time frame, at any point , we hand pull/push the screw rich/lean of its position..if we pull it foward and the rpms go up and the engine smooths out , we are too lean , if we push it in and rpm go up , we are too rich ..
the ideal settings are when you push the screw in the very slightest and the rpms increase is barely noticed and then drop...a good way to sink this in here is by adding as little air with the air bleed screw at the intake to balance out the air being sucked in at the thermo valve.
For those that have operated a carb choke , you know how you could get your cold car to run great when cold by knowing just how much to pull that knob.[every car had its little secret]..well, what you are doing is setting the perfect a/f mix that the engine likes at that low temp, ie., a rich, but balanced mix...that is what the cold run mechanisms are doing, and it takes some tinkering to get them right.
If it seems to run too rich when cold, a quick check of the pump
air filter is a first on my list..a dirt clogged filter will cause an overly rich/low rpm warm-up in a heartbeat. If , even after warm ups , one still has rich running conditions and ALL OTHER adjustments have been made, the barometric compensator is famous for getting weak with age.. this can be remedied by some shims removal, but be careful here .. better rich than not..
The problems with Mechanical Injections is that all A/F mixes are dependant on pre-measured mechanics and if any are off, the system has no way of correction, as in newer 02 sensor, info feed back electronic systems... The pump just assumes that the throttle is correctly at a predetermined set degree .. the advantage to all this is that we can tweak these adgustments to our own likeing and they are a Mechanical Marvel that one just falls in love with....
