will my xr400 die

i put full exhaust system uni filter on my 99 xr400 it has STOCK jets :) when i rev it it pops crackles backfires but goes hard do i just leave it and let it get wore in abit and it might come better?

No, it won't get better. You most likely are running lean. You can't open up the exhaust and airbox for better flow, then cheap out and not rejet and retune the carb for the new flow characteristics. You could end up paying dearly for that mistake.

i rang my dealer abit earlier he quoted me 300 - 400 to rejet and tune, is that normal price cause i thought he was joking. should i try a another shop?

No &%$#@!ing way! Do not let your dealer rip you off like that! Jets are about $5 a pop and very easy to do yourself. If you need help, I'd be more than happy to guide you through it.

If you put the pipe and filter on yourself no reason you can't jet it. Jets are cheap and your dealer is a thief!!

If you don't know what you're doing, it will turn out to be a lot of work to save $300.  


Hopefully the dealer will be able to get the jetting close, but how will you, or anyone here know when it is optimally jetted?  

Both good points BR. But the most important thing in saving that 300-400 dollars is learning to do the job himself. That's why the good folks at TT are here to help, to guide and prevent a simple job from becoming a lot of work.

Learning jetting is a great idea, but as you know, there's a lot more to it than threading in a couple of jets.  It seems many riders are changing jets without addressing the basics.  An entire volume could be written on the subject and we keep doing that over and over. LOL.

OP should look up jetting and plug reading basics and still do it himself. $300 is downright ridiculous. Hell, I'd do it for free to save this guy getting ripped. It's a little time consuming to get right but it really isn't difficult.

OP should look up jetting and plug reading basics and still do it himself. $300 is downright ridiculous. Hell, I'd do it for free to save this guy getting ripped. It's a little time consuming to get right but it really isn't difficult.

+1, Knowing where the guy lives and his elevation would narrow down the jetting a BUNCH, then tuning could be walked through quite easily, IMHO.

I'm in Australia, Tasmania and im at approx 100m above sea level

Lucky for you, I'm in Australia, up in north QLD and I'm 180m above sea level. When I did my bike, I put a 60/160 in as a base tune. And ran it for a while and read the plug and it was good. Being in Tas, I would give the 60/160 a go and then go from there. But please don't let yourself be ripped by a dealer. Hope this helps.

Dam 300 bucks is a rip off i watched a youtube video on how to clean a carb got my jetting from the people on thumpertalk whole thing took like 2 hours. Getting the carb out was the hardest part but even that was alot easier than i thought. Before this i had never even seen a carb pretty dam easy job to me. Assuming nothing is broke.

How about that spffy new Mikuni pumper carb from XR's only - supposedly cures all woes... I am going with one on mine after a top end job.

Every situation is unique. However you can get close and XR400s will run great.
You can put in a 60 pilot and 160 main, then be in the ballpark for jetting. People jet these all over the map without harm, but your bike is lean now and that isn't good. Want the jetting perfect? That takes work. Want close enough? Use the 60 / 160 jets.

96-97 sold with 62 pilot, 162 main, different slide, different needle. Really rich as shipped. Honda expected them to be uncorked.
98-04 sold with 52 pilot, 142 main. New slide and needle. Shipped really lean. Honda expected it to remain corked up.

Gordon's mods is mainly about uncorking and using the 96-97 jets.

For 300, I would expect it to be tuned on a dyno.

These guys had a Jetting kit with several jets for an XR400.  


This is a good deal if you need the needle or want tuning instructions.   



The XR400 kit



If you don't you can buy several jets from RockyMountainMC or the TT store, or who ever.   Don't forget, you can buy jets from "road racing" or street bike stores.   I have found dirt bike stores have limited jetting inventory.  But a road race tuner, like Factory Pro, will have many.   400cc x 2 = 800cc V-twin.

Edited by Kev_XR

by uncorked do you mean taking the snorkel out?

"Uncorking" is just a general term for removing any intake and exhaust restrictions that keep the motor from flowing at 100%. 

60/160 is a good starting point to protect an uncorked 400 from dying a lean death.  I jetted my buddy's 400 somewhere in between (58/148?) with no uncorking. I also changed to the 49 state needle on the third position.  It's not dialed in but it's not running too lean and it starts easier than before.  


We ride long distances in hot weather where sometimes there are no gas stations, so mileage is an issue even with four gallon tanks. He thinks his range dropped  from 220 to 180 miles with that jetting change.   He generally runs low RPM on the pilot and needle to save fuel.  The richer mixture runs cooler.

Factory Pro was so tired of XR400 requests back in 1999, they offered to dyno my XR400 for free.   I can't remember why I turned them down.  I think I didn't want to have to mount a street tire.   Dumb on my part.


My FAQ has the stock jettings for the USA.

Ballpark jetting for various mods, such as Unifilter, remove intake snorkel, and leave in the one piece exhaust.


XR400's are air cooled, oil cooled, and fuel cooled.

If you are willing to pay that kind of money for rejetting a carb you can purchase an electron carb for your 

XR for about that same price there by eliminating the constant hassle of rejetting if you ride at different 

areas with different altitudes etc.

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