Ok so I bought a 1 1/2” holesaw and did the z1 but I don’t see how people complain about the noise. I see not much difference at all from stock. In fact that set up I had on before ran a lot louder and thumpier. I think it had more grunt too. I need a new speedometer cable so I couldn’t record speeds but it felt much the same as stock.. that airbox delete I feel made a stronger bike with the 47.5 and 112.5 in it. Made a lot more carbon buildup so reliability prob went out the window and you could feel more vibration from the power I guess. I removed snorkel and drilled holes into the side and that helped a lil more.

You typically don't shim the needle in the XT. The 130 main is enough on it's own. Needle shims with the 112 main makes more sense as the bike normally goes very rich when shims are added.

I got a noticeable increase in noise from doing the Z1. Nothing you can do to the XT225 is going to give a noticeable increase in power if it was running right to begin with. Jetting will make the biggest difference, but only if it was way off. I notice a slight loss in power when I ride mine from 1200 feet to over 8000 feet, where it is a little rich, but it is not a huge difference. If it is lean you will usually get a hesitation or flat spot when you open the throttle. It will also run hot. I have never shimmed the needle on any bike. But, I have also never altered the intake. while I have had maybe 3-4 bikes with an aftermarket exhaust (my Sportster came with aftermarket slip on mufflers) but I leave the intake alone. The stock intake is quite good at removing dirt from the intake air. It also has a designed in restriction (on the XT that is the snorkel and the size of the hole where the snorkel goes. It is not the size it is by chance, it was carefully engineered that way to function properly. Once you remove or modify the intake, you have opened up a big can of worms that you may never get sorted out. Carburetors, by their nature, have a limited tuning range. You have the main jet, pilot jet, and pilot air screw. That's it. If a modified intake allows significantly more air into the intake, it may be impossible to tune the carburetor to work right over the entire engine operating range, from idle to redline. It may be too rich at certain speeds, and too lean at others. And every setup is different, and will require different tuning. I have always found completely stock to work better than anything else.

When I installed the pod filter on my GS500, I got a huge increase in intake noise.

I'd guess he had the same with that remote filter setup. So putting the airbox back on would quiet it down but the Z1 makes it louder so the net effect may be a wash.

I installed the stock air box and removed the snorkel, that gave a little boost in air flow. I imagine opening the exhaust does in the same manner, it runs great. Another question, that spiral piece on the end of the spark arrestor. Is that necessary? I feel they does deter sound and back pressure as well

Yes, the angled baffle vanes are part of the spark arrestor design. These impart centrifugal force to the outgoing exhaust gas. This throws any sparking embers to the outside while the exhaust gas goes out the center.

This is what qualifies the muffler for the USFS APPROVED SPARK ARRESTOR stamping on the tire side of the muffler.

AFIK these have nothing to do with exhaust sound level.

After doing the Z1 mod, I did run mine for a few minutes in the garage before putting the spark arrestor back. The sound was lower pitched, but probably not louder. Whatever you do, don't ride the bike off road without the spark arrestor. I ride mine both in the desert and in the forest. And all it takes is one spark to start a fire.

I took the spark arrestor out and ran it up and down the street. I love the deep thump at idle but when on the throttle it’s kind of obnoxious but still fun to blare through town. So I may do that to annoy the towns people sometimes. I took the screen off. No change at all. Put snorkel back on and chopped. Quieter, always had holes drilled in the side, might be slightly quicker take off though as it slides better than snorkel off. I’ve just been playing with everything today. I love the way it sounded and ran with the 47.5 112.5 but hated the mpg (id say around 50). With the 42.5 130 z1 its an easy 70+. Well that’s my prognosis, hope you enjoy. I want to make an end cap which makes the deep sound come alive or modify as I have 2

Obnoxiously loud pipes aren't the best way to make friends, just saying.

Agreed. And don't modify the spark arrestor in any way. It's there for a reason.