California WR400 exhaust mod help

I had asked whaat mods I could do for free and received a wealth of info. One of them was to hollow out the stock exhaust and I even got pics and links but in one of those links, it says that the California bike exhaust can not be tampered with. Can anyone clear this up for me regarding the California exhaust pipe. The end spark arrester comes off the pipe and inside I can see a large hole coming out of a block off. Do I just drill holes in this block off? Help, I hate to ruin the exhaust and do it wrong. Thanks again.

When you are looking down the end of the pipe you should see a baffle that runs down the middle of the pipe making the hole smaller. Now if you take the whole end off and turn it sideways you will see that it is held in there with two small rivots on each side. You have to drill out those rivots in order to get the baffle out of the middle. Once you drill them out use some visegrips to pull it out.

On my 06 WR450 I went ahead and got a new insert with a larger hole instead of drilling out the baffle on the stock one. It was a bolt on part that took about 5 minutes to complete. I think that was about 30 bucks. This way I have the stock one on hand if I ever end up needing it. maybe something to consider if your not 100% sure.

Furthermore, as far as I know In California all you need to have is a spark arrester and be able to meet sound requirements on BLM land. By changing out the stock end and or making the stock hole bigger you should still pass sound easy. And as long as you don't take out the mesh screen you will be good to go on the sparky as well.

Hope that helps

So I drill out the rivets that hold the plate inside that seems to restrict the flow down to about 24mm or so out and remove it completely right? Then reinstall the sparrky end and I'm good? Thats it... Theres nothing else behind that plate that has to come out also? I don't see rivets on mine, im assuming I can just drill holes in that plate so it doesent restrict as much flow right? Thanks again.

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