Completed the Z1 mod yesterday but made a small adjustment/Hybrid. Some Z1 posters were not happy with the new noise level after they did the mod and I did not want a big increase in the sound level either. I read in a much much older post where someone's bike had just the bottom edge of the baffle surface detached and lifted allowing more exhaust into the spark arrestor chamber. He was very happy with his exhaust.

What I did was instead of drilling the large 1 1/2" hole I looked inside to see where the exhaust was entering the spark arrestor chamber. Looking into the exhaust from the rear, there is a hole on the right lower edge/wall about 5/8" in dia. So I tried to detach the back of the chamber directly across, left upper edge, to balance the exhaust entering into the spark arrestor chamber. The back surface would not move so I punched a hole about 5/8". Results are just what I was looking for in sound, not overly loud. In fact I could open up the hole a little more for more sound and I would be OK with the noise level. I have ridden the bike only enough to check the sound have no idea if there is a hp improvement, hoping balancing the exhaust pressure entering the chamber will have a positive effect. I also did not want to open up the exhaust too much as my bike starts easy and has no carb issues. Will update performance after my next trip out.

rocmoc n AZ

Sounds like what I did with my last two XT225s. Instead of drilling a hole I used a long punch to break the bottom edge of the interior baffle lose and lift it a bit. Worked a charm for me, and the bikes were less restricted exhaust wise as a result.

Yup, sounds like we went the same route.

rocmoc n AZ

Last Tuesday, I had an opportunity to hear what my 28mm Z1 mod sounded like as a pedestrian (walking behind someone else riding the XT), and as a passenger, without earplugs. I was surprised at how innocuous the sound was. The 270 pound guy who rode my XT out of the wilderness, who has a BMW G450X, was also surprised at how well the XT handled his considerable load, even with a 16T countershaft sprocket.

By the way...the Z1 mod (and similar) should have no effect on starting.

Alexd