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Jetting questions(s) and carb question

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As I stated in another post, I'm working on getting my bike plated, mostly for fireroad riding, etc. but also, once in a while, to ride to work.

I know I need to quiet the bike down, so I've purchased a stock muffler off of eBay. I priced one at the dealer, 400 bucks, eBay, 50 bucks! You gotta love the internet. If I put the stock muffler on, I know I'll need to rejet, but I've not ever before done any jetting, so I'm in new territory here.

What would proper jetting be for my XR 400 with the following setup?

FMF Powerbomb header.

Stock muffler (not yet modded but that may come later)

K & N filter and removed snorkel.

I have the stock jets, at least I think I do. One has the number 158 on it, the other looks like 160. I'm not really sure what size jets are in the bike now, but I know the previous owner rejetted with the exhaust upgrade.

Any thoughts on how much quieter I'll run with the stock muffler? Or how much less responsive the bike will be?

I guess I'll have to see, but I want the bike to be quiet. If I have to spend money on a carb to get the power back, I'd rather do that than have a loud bike.



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The stock muffler will be more than quiet enough. I have a stock muffler on my 400 and run #155 main and #55 pilot. Snorkel removed and UNI filter. I do not have the powerbomb header though. #158 may be fine. There was a comparision of mufflers somewhere and the stock muffler had better low and mid range torque and less top end than the aftermarket ones.

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