I am in process of completing restoration of a 1973 BMW 2002 tii. In order to complete
this project and tune the engine I am requesting suggestions/ tech advice on how
to sort out the Kugelfischer Fuel Injection System. The issue at present is the motor
runs excellent upon start up, however after reaching operating temperature. The engine
proceeds to increase fluctuating RPMS from 750 to 4500 then quits running and
will not start until temp is reduced to cold. This car has been seen by various "old school
BMW techs" for the past few years and they say " I have never experienced this situation in
all my 40 + years" after that the situation is "mox-nix"
Instead of throwing in the towel I am determined to hopefully locate an experienced tech
that can tame this beast" I live in Colorado and would prefer a knowledgeable and competent "old school BMW tech" located in the general vacinity. CHEERS
I am distributing your concern internally to see if I can find a specialist in Hagerty that can assist. That said, when was the last time that Kugelfischer rebuilt? It might be as "simple" as taking off the Kugelfischer and shipping it to one of the (few) rebuilders so they can go through the entire unit.
Fluctuations in idle on a tii are usually caused by the idle mixture being too lean, but I'll agree that 750 to 4500 rpm is a BIG fluctuation. Ignoring the size of the fluctuation for a moment, idle mixture is adjusted by the tiny screw inside the "tuna can" at the top of the throttle body. Backing the screw out (turning it counter-clockwise) makes the mixture richer. Tiny adjustments should be made. On every tii I've ever owned, which is something like 12 of them, you find the point where the idle no longer hunts, and where, when you blip the throttle, it doesn't drop down low before recovering.
The fact that you say the engine runs well at startup and that the problem begins once it's warmed up makes me suspect something in the warm-up regulator. Its job is to give the engine extra air at cold start and during warm-up (and to move the enrichment lever on the Kugelfischer pump, which gives it more fuel). Once warmed up, the piston in the warm-up regulator should rise and move the enrichment lever so the screw on the enrichment lever (the "verboten screw") is resting on its stop.
If it's not curable via mixture adjustment, and if the warm-up regulator appears to be working properly, the problem may be a vacuum leak. A smoke machine test may be helpful, as it may uncover a bad intake manifold gasket. But be aware that there is some amount of normal air leakage through the warm-up regulator, even when the piston is fully extended.
Have you or has a garage put an exhaust gas analyzer into the tailpipe to see how rich or lean the mixture is when the idle fluctuates?