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Hi there.

Inexperienced when it comes to jetting for new exhausts.
I have a 1981 Kz 550 D-1 (GPZ550) and I'm looking to get a 4 into 1 straight yoshimura pipe ( pic below ) Has a baffle i believe.

I'm on the stock 22mm TK carburetors. I would like to stay on the stock airbox (if possible or suggested).

Any suggestion on how many sizes I would need to jet up?

I've got the same bike and situation as you and would love to know as well!

I didn't see this thread back in 2019.

But with a factory airbox, a mild exhaust can be run with the stock jetting.  It may be a slight bit leaner, but should still be fully rideable, especially in warm weather.  A wide open exhaust or really free flowing one may make some backfires and such on decel, and may be a bit jerky on a steady light throttle cruise.  A couple sizes up on the main from will often be enough and maybe even a bump to 34 pilots.  Make changes to one thing at a time.  I would try the main first since those are easier to get.  The airscrews should be adjusted properly as well, using the lean-drop method.  They may need to end up a bit further in (richer) than they were with the stock exhaust.