Upjetting an otherwise stock bike, and a top end rebuild

Something I've been thinking about, since the bulk of "emissions control" from the early 80s consisted of running the bikes lean from the factory, would going up a single pilot/main jet with no other mods improve performance? Also, what size/category/thread pitch does the XJ650 have, for ordering replacements?
I'm in the middle of a top end rebuild on my 1980 XJ650, doing valves, light head porting, cylinder honing, and replacing all the relevant gaskets (whoever worked on the bike previously didn't put in exhaust gaskets). Has anyone done anything like this? I plan on getting it on a dyno once it's done, so I'll probably be upjetting anyway, but I'd like to hear other people's thoughts.

 

I also would like to hear peoples thoughts

 

If you are truly going to put the bike/engine on a dyno, I would wait till then to rejet, you may find out it's pretty well optimized as it sits.

 

You’re pretty much on your own here - guesswork is pointless, but it’s what most people use. Do you know what you’re doing when it comes to porting? You can really cock up something that isn’t that far wrong if your not careful. Aaaand, to be honest, how much might you gain? 10% ? If you’re good, and lucky....
If you’re serious, you’d want to fit a hi flow air filter and a 4 into 1 exhaust - even more head scratching, but then you might exceed the 10% I guessed at above. If you’re good enough to get that far you don’t need help from a forum, where most people just want to keep stock and ride...
The hi flow air filter really upsets some cv carbs, and can take a lot of doing to sort (I used some bs32 mikuni cv carbs from a 600 on my 650, and they were fine with pod filters, and equally fine with the 600 air box, so no hard and fast rules there though - (the lack of suction pressure upstream of the carb will always cause the piston/slides to rise too soon, so weakening part and full range mixture, to a greater or lesser extent, and up jetting doesn’t always cure this).

 

I think this link came from somewhere on xjbikes.com I found it very helpful to understand everything that goes into jetting your carb's. It made me realize that this is not a job for a weekend warrior. Trust the engineer's that designed it in the first place.

FactoryPro CV carb tuning guide

 

That’s probably one of the best guides I’ve see. It does not cover early slide lift due to increased pressure at the carb mouth (caused by high flow air filters), which if added to porting and exhaust improvements could mean the slide hits top well before maximum power, thereby leaning mixture out, no matter what is done with jets.
(Someone spent some time deciding on the best spring rates for these).
Still a good guide though.

 

I'm really only going to smooth out edges and get rid of the casting imperfections. I figure I may as well while the heads are off.
I have them off because the bike had less than 100psi compression on all cylinders and just felt weak in general. I also kind of wanted to rebuild it just for the hell of it, as you don't need the engine out of the frame to take the head/cylinders off.
Still going to use the stock airbox, maybe opening up the airbox inlet hole a little.

Maybe I will, it'll still be good to check it out though. Either way, I'll definitely post the dyno charts here.