@bowser881
Yeah, these old bikes (I have a 78 550K) were tuned to use the stock air box and whatnot. I think the frustrating part is the tuning part. If you're willing to put in the effort and try some things I think you'll be able to figure it out. I'm in the middle of my build as well and the previous owner had pods on the bike and so he also changed the main jet, but then he let the bike sit for a couple of years. I'm in the process of getting it cleaned and seeing if the engine will fire but before I start fiddling with the tuning, I am going to try to get it to the point back when the previous owner had it running.
Anyway, good luck.