Hi, I'm from Spain and I'm starting a similar project. The GZ250 is called "Marauder 250" here, and we've got a forum in Spain too:
www.maraudercustom.com, successor of
www.marauderos.org. I think that you got your workshop manual from there.
Related to this topic, I've purchased several main and pilot jets and a new jet needle to try it. I've already removed the air filter box (mixture becomes so lean) and I'll replace it for a "powerfilter" (our carb's mouth is 50mm diameter) and then I'll carb the bike. By the way, there's no need to remove anything to gain access to the carb and the jets.
You can view the carburettor config of my GZ250K6 in the last column of this chart, extracted from the workshop manual.
Also, the product codes of the jets are the following:
Main jet - N102.221
Pilot jet - N224.103
or VM28/486
I'll share with you my experiences as soon as I'll test the stuff.
Sorry about my English. :blush: