Sounds well known...
If you car is idling & driving fine up to 4000 rpm, everything with the CIS system looks fine.
Maybe the distributor, but I doubt it.
I suspect the fuel pump! I had a worn fuel pump and a bended fuel line when I got the car. Took me half a year to figure it out. Enough fuel for normal driving, but not good enough for full boost. Car kept stalling at 4200 RPM (like a hit in your a__)!.
So check your fuel system first before fiddling around with the CIS!
Jens
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