OK the Service Manual does not say what size the wire is. But, it gives the size of the tiny central hole in the Pintel. You will need to use a Wire that is undersized or it will indeed stick in the hole and sometimes break off.

The origional Nozzles had a 0.15mm Central Hole
In Nov of 1981 the hole size was changed to 0.20mm

Also where I worked between 1975-1980 we used Carburator Dip to loosen the Carbon on Injectors and Turbo Chargers. I do not know if the newer less toxic stuff they make now will do the same thing.

A Ultrasonic Tank could also work with some chemical cleaner.

On eBay they have some ads for K&S ENGINEERING wire.

In both cases it would work better if the central Hole was cleaned out with the Wire first so that the Chemicals could actually get inside.

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84 300D, 82 Volvo 244Gl Diesel