New Exhaust for a XR400R...Should I??

The deal is, I was riding this past weekend and ran upon another XR400R that sounded much better than mine. After talking to the guy, I found that I could gain a pretty good little jump in hp (as well as get a better sound) by applying an after market muffler.

So, here in lies the questions:

-Can I replace just the muffler to see a boost in hp?

-What are some mufflers that you would recommend?

-Can someone explain a bit about jetting?

-Is jetting necessary on the XR after replacing the muffler?

-How much should I expect to spend?

-Do I need an after market header or is the muffler enough?

-What about spark arrestors?

Sorry to beat you down with so many questions but, as you can see by my profile, I'm a newbie :)

Thanks to everyone for any help you offer.

Here's the short answers... I'm assuming you're trail riding and not racing moto...

1) Replacing the stock muffler will give you a good boost in HP. You're not gonna turn it into a 426, but you do get an increase. There are also inserts offered by Baja Designs and other mfgs. that replace the stock core on your existing pipe. They give you modest increases in power and don't cost alot.

2) I had a Megamax on mine, and liked the power. I've heard good things about the Yosh pipe too but its $$$.

3) Type 'jetting' into the TT search and you will certainly find all the info you need.

4) Mine didn't need jets and ran fine (0-5,000 feet).

5) $200-400. Check the TT classifieds and you will probably find a nice used unit from one of our fine members.

6) Stock headers are OK for trail use.

7) Because of the nature of the bike (trailbike), most if not all of the replacement mufflers for the XR have spark arresters built in.

Good luck with your mods!

Try doing a search of "gordon's mods" for lots of tips to unleash the power of your XR4!

I put a Vortip exhaust tip in and it helped out alot-- and sounds healthy as well.

You're going to have to rejet, but the jetting is pretty straight forward. Check out Baja Designs and also the Gordon's Mods for the best set up.

You have to do both to get anything out of it. Also, get rid of the snorkel if you haven't already.

Good Luck!


First, my question: Do you live in California?

So, here in lies the questions:

-Can I replace just the muffler to see a boost in hp?

Yes, but your carb may be lean. It will be lean if you have a 98 or newer California model XR400.

-What are some mufflers that you would recommend?

If you live in CA, there will be a sound limit of 96db starting in January. If you don't pass the sound test, Mr Ranger says you don't ride.

I think my friend was running a FMF Megamax and seemed decent. I'm not sure if is under 96db.

-Can someone explain a bit about jetting?

More air requies more fuel to make the same mixture ratio.

Bikes don't run well with too much air or fuel.

Since adding a pipe, changing the air filter, pulling the intake snorkle can upset the balance, you need to re-adjust the jets inside the carb.

-Is jetting necessary on the XR after replacing the muffler?

For the CA model, YES! It came lean from Honda to make it green sticker compatible.


-How much should I expect to spend?

$10 to $200.

$10 - New pilot jet, new main jet.

$26 - New pilot jet, new main jet, A16A needle if you have a CA model.


$45 - Performance cycles in San Rafael, CA sells a kit with their own needle, serveral jets, hex screws. A good kit for experimenting with your jetting.

$160 to ??? Take the bike to a shop and have it professionally jetted.

-Do I need an after market header or is the muffler enough?

-What about spark arrestors?

You need one to ride off-road.

Gordon's Mods

You have to open both ends up to get the full effect.

Stock Jetting

Component............96-97All States..98XR Calif.....98 49 States

Main Jet.............162..............138............142

Pilot Jet............ 62...............52............52

Main Air Jet.........#100............#90............#90

Needle Jet...........10 mm..........10.5 mm....... 10.5 mm



Pilot Screw......2 1/4............1 5/8............1 1/2

Note: The 96-97 stock jetting was designed to have the user remove the intake and exhaust inserts. The newer stock jetting was designed to leave them in.

Remove airbox snorkle, Uni-Filter, stock exhaust endcap

(From MXA magazine and local Honda dealer)

155 main

A16A needle, 3rd clip

55 pilot

Remove airbox snorkle, Uni-Filter, Baja Designs exhaust endcap

162 main

A16A needle, 3rd notch

60 pilot

Also, see "Gordon's Mods" on the XR400 Group at

I'm at Sea Level, near San Francisco.


Here is an old email on jetting:

The factory service manual is Excellent in my opinion and well worth the money spent. Even though it won't teach you how to jet or tune your carb, it has excellent diagrams and covers a lot of important information. If you want to learn more about tuning your carb, there's several good books out there on this subject, but there's also a lot of excellent information on the internet such as from these links...

Here's some links about reading spark plugs that may be helpful in regards to carb tuning...

Great compilation of XR4 mods and useful links! It took me hours to find all that stuff.


Wow! You guys are incredible.

Special thanks to MXbob60, malibu27 & Kev_XR!

Y'all gave me some great info to work with (and quickly too).

I appreciate it!

You didn't say what year it was. The earlier ones had a removeable baffle. I put one on my 00 400 and followed Baja Designs jetting recomendations. Chuck the vortip though. Anyone want to buy mine? Also gently clean up the rough weld at the exaust flanges.


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