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If you do the reading, opening up the fuel distributor is not advised unless you're prepared to go the whole distance. Only once was I tempted to dissassemble it for an inspection and cleaning before doing the reading to realize what was involved, that a rebuild kit would likely be needed and the C/O re-adjusted. It was at that point I started to occasionally use fuel injector cleaner additive in the tank to help keep the injectors from fouling on a well worn engine. Poor and uneven injector spray patterns were my basic issue at that time, probably from using cheap gas and doing too much city mileage.
I think Nahtanha is likely correct. My reading also suggests that when one port is clogged that varnish on the port screen is a likely issue for a car that's been sitting for a long time. But for a car that's been sitting, there's also the chance that rusting has occurred in the distributor which could also be retricting flow, blocking a port or fuel line. If one port is fully clogged I would expect the others to not be far behind. Although you could try running the pumps and measuring the flow rate out of the other injectors to see if other ports are starting to plug, I really don't see the point.
As many of us know, getting rid of varnish is not a simple task just using cleaners, especially cleaners that won't destroy rubber seals. My initial thought for you was repeated overnight soakings and attempts to back flush using a syringe in the hopes of at least partially opening up the blocked port using a top injector cleaner concentrate like Techron, Red Line, Lucas or Gumout, maybe even SeaFoam, but I just found something better for you.
Here's a good YouTube video on rebuilding the fuel distributor where one of the steps shown is pulling the screens out for cleaning with a long threaded screw. If you only need to do the port screens then you will not have to fully dissassemble the distributor or readjust the C/O. It starts at the 6 minute mark.
https://www.youtube.com/watch?v=ySdtAHvKEeE
There's no audio and you may have to bear through and skip a few ads if you don't have an ad blocker. In case that video link should change or disappear, it's on the Restoration Apprentice channel under the title "Bosch K-Jetronic Fuel Distributor Rebuild // 1985 Porsche 924 Restoration Project"
Maybe just pull the blocked one first for initial inspection to see if that's the problem. If not then prepare yourself for a full overhaul. Kits are available, which don't appear to include the screens.
The video later shows cleaning the screens in citric acid. If you do the reading, citric acid is supposedly slightly better than vinegar (acetic acid) for dissolving varnish. You may have to do a little hunting for citric acid. It can often be found in powdered form in places like health food and bulk food stores. It's a weak acid so don't be afraid to make it fairly concentrated.
If you want to try soaking and flushing the entire distributor I would only use fuel injector cleaner or gas. Remember to blow any residual cleaner out with lower pressure compressed air (like the 35-45 psi that we know the fuel system is designed to handle) before firing up the engine.
Hope that helps. Please post back with your results for the benfit of others.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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