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Kevin's XR400 FAQ

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If you own an XR250, many of these tips will apply, however, the carburator jet sizes will be different.


It really helps others answer your questions.


I will fix them as time allows.

Until then the Search Feature and enter "kevin's xr400 mods".

The results will bring up most of the links.

Here are some frequently asked questions I have answered before.

Which XR should I buy?

The longer the straights, the taller the hills, the deeper the sand; the bigger XR you want. The tighter the trail, the smaller hills, firmer terrain; the smaller XR you want.

The XR400 has a great motor that will pull you almost anywhere. You can be sloppy on a hill climb on an XR400, where you have to keep the 250 singing. The XR400 weight is most noticable when you drop it or try to stop it going down a long downhill. (Moooomentum!)

The XR250 feels like a mtn bike compared to the XR400. My friend rode his XR250 for years before decided he needed more power. Even then you can add a 300 kit and get good power.

If you were heading to ride fireroads in Baja, I'd tell you to get the 600/650.

To the tight woods, get the 250.

A lot of both, the 400.

Dual-sporting? Go bigger for more freeway, but don't show up at the trailhead with too big of a bike.

All of the XR's are great. Pick the one that fits your needs.

Gordon's Mods for XR400 (Uncorking the bottle up performance)

Gordon's Mods for XR400

XR400 History

The changes to the XR400 have been listed here several times. This list appears to be complete.

In addition, HairyScary discusses how to tell if a part has been updated by the part number. Good tip!

XR400 history

Getting the Spark plug out

It seems the MotionPro spark plug socket does not work on the XR400R, but works on the XR250R.

There is an OEM tool kit being sold on eBay that seems to work.


717448 XR400 oil change

Here is a way to make changing the oil much cleaner.

This tips is really handy if you have a skid plate.

XR400 oil change

XR400 FAQ by Paul Gortmaker

Paul usually has very good info.


Small bolts

BE CAREFULL with the bolts on the oil filter cover!

An oil covered bolt will not torque at the same rate as a dry bolt.

The friction doesn't build up, the force simply builds until the threads strip.

This is the reason many people strip out these bolts.

Here is an execllent website on bolts, oil, and misc values.


Did you ever wonder why a 8mm box wrench is half as long as a 18mm box wrench?

It is shorter as most 8mm bolts cannot take very much torque.

I highly recommend getting getting an 1/4" socket set.

I bought the Craftsman set at Orchard (owned by Sears), which tends to sell them for less.

What is the Snorkle?


This place has a description and pic, it's easy after you pull the seat. I siliconed a piece of coarse screen (fiberglass) over mine to keep bugs and stuff out. - NORTEXT

717439 XR400/250 Pre-Filter

After pulling the snorkle, there is a big hole on the top of your XR400. My friend showed me this prefilter trick.


767409 XR400 Engine Bog, Pilot jet, and the Fuel Screw

On XR400's twisting the throttle from fully closed to wide open will cause the engine to "bog" or in some cases die.

Engine Bog, Pilot jet, and the Fuel Screw

831305 Valve adjustment (Am I retarded...)

Inspect and adjust valve clearance while the engine is cold (35C, 95F).

Valve adjustment

389095 bigger jets (Lists stock jet sizes.)

96-97 XR400's were jetted assuming you would remove the intake and exhaust snorkel.

98 and later XR's were jetted assuming you would leave them in.

bigger jets

739907 Cheap Tool for Setting the Fork Oil Height

There are some really nice tools out there for doing this job.

This tool costs $4.49 at Kragen.

Cheap Tool

392932 high altitude jetting

There are two big factors for jetting, elevation and temperature.

high altitude jetting

Allen screws for the XR400 carb

This lists the screws you need to convert the XR400 carb to use allen screws.

Allen screws

Screws for the brake and clutch after removing the stock handguards

TBD - There is a post with the shorter screw part numbers for after the stock handguards are removed. Use search.

Very quick engine hop up


This is a very minimal change that should take less than an hour.

Most of that time is removing the float bowl (3 screws).

If you decide to do the full "Gordon's Mods" later, you will need to replace the jets again.

o Pull the intake snorkle.

o Add a UniFilter.

o Pilot jet to 55, main jet to 155. (Assuming sea level and moderate air temps.)

Source: Motocross Action magazine.

Quick engine hop up


Gordon's mods

Baja Designs Baja Baffle with 96' spark arrestor.

Pull the intake snorkle, UniFilter, 60 pilot jet, 162 main jet.

(Depending on altitude and temp.)

What to add to a new XR400 or XR250?


Acerbis wrap around style handguards (saves levers and bars as they don't dig in)

Baja Designs skid plate (Made by Utah Sports Cycle)

Acerbis fork/disc protector



Grease headset and rear linkage

Spend you money on the suspension, not a pipe!

First get some stiffer fork springs (96-97, 98-99 years)

Fork revalve (cost: 2 qts of oil & time)

Shock revalve (cost: oil, nitrogen, shim stack, friend who knows shocks)

Jetting for Altitude (XR400)


Assuming at sea level and 68 degrees, you would use a 60 pilot and 162 main.

At 5000 feet and 68 degrees.


Jettting correction:

5000 feet and 68 degrees.

Main 0.96 * 162 = 155 -> 155 main

Pilot 0.92 * 60 = 50.6 -> 55 pilot

Due to your elevation, you have less air and less fuel.

Your bike will not behave the same as a bike at sealevel.

First, check the fuel screw. If it does not affect the idle speed, you have the wrong one.


kevin's xr400 mods

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nice work Kev !

I've read alot of these thru the years, but its really nice and handy that you took the time to organize and present this. Great reference !

thanks !

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[*]URL titles are now shorter.

[*]"Oil change" link now has images from Photobucket.com that are visible.

[*]"Pre Filter" link now has images from Photobucket.com that are visible.

I don't have the ability to PIN this thread.

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Great compilation, thanks! I'd never seen a couple of those threads before.

Think I'm going to try out that pre-filter you came up with. I absolutely HATE having to clean out the inside of my airbox, and that should help alot.

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Carb jetting links thanks to Quadsan

You'll know you need to rejet if your bike us running abnormally hot, or if its pinging, knocking, surging or blubbering on acceleration, or if you see signs of running too rich or too lean when checking your spark plug, etc.

The factory jets are close enough to get the bike working pretty well for most stock applications, but to get the bike running near optimum for specific bikes with aftermarket parts and specific environmental needs takes plenty of time/patience and or experience along with some trial and error. If you buy a less restrictive aftermarket pipe, then the instructions that come with it may offer specific jetting advice to help you minimize the guess work. You can also go to a shop that specializes in dyno tuning and they'll try various jetting combinations to find a combo that makes the most power for your bike.

Once your bike is tuned nearly perfect, you then have a good baseline to work with. From there you can use correction factors to determine what jets to use when your riding location changes in altitude or temperature. Humidity also affects jetting, but not nearly to the extent that temperature and altitude does.

I used to jet bikes using the seat of the pants method and it worked very well. It helps a lot to know what an excellent running bike feels like and from there in combination with your previous jetting experiences you'll be able tell if the bike you're running is too lean, too rich or just right.

I basically used the method I described in the long winded post above to find my optimum jetting. I'd first make a run at WOT, then shut off the engine, pull the plug and check it out. I used to use a magnifier I had along with a bore scope light for checking the bores of my guns and it worked well enough to see what I needed. If the mixture ring was half way down the insulator (indicating I was still running rich), then I'd install a leaner main jet the next size down and make another run and so on. I'd keep making runs and changing out the main jet until the mixture ring nearly disappeared on the insulator where it joined the shell. At this point you could tell the bike was truly running well because it just had that extra crispness to it when it was opened up all the way.

From there I'd mark off the throttle positions in relation to the throttle slide and make a number of passes to find out what the spark plug showed and adjust my jetting accordingly. There's definitely an element of trial and error involved in this process even for experienced tuners.

I don’t know if I’d trust everything the dealer tells you and that’s why it’s a good idea to become a bit savvy on these types of issues. There are plenty of very knowledgeable dealers around that offer excellent advice, but there are also plenty of dealers that may unintentionally steer you in the wrong direction.

If you’re comfortable taking your carb apart, then I’d find out what jets are installed so I had a baseline to work with. Changing the main jet is a piece of cake like Team Burk said. Changing the other jets is more involved, but just getting the main jet right is a step in the right direction. Most of these guys who have

Instead of doing all those spark plug checks and changing out jets until your blue in the face, you could always copy someone else’s known good XR250 jetting if the bike & riding environment is setup similar to yours. If worse comes to worse, you could always put your bike back to the way it was.

Here’s some links on carb jetting that will offer more info.










Here's some links about reading spark plugs that may be helpful. In the first article from hondaxr, I used the term base ring when I wrote that post, but it’s also known as the fuel ring or the mixture ring. One of the best articles I’ve read about this topic was from the late Gordon Jennings, so give that one a closer look (it’s the first of the next three links).




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NOTE: The information below was compiled and posted by Paul Gortmaker (I'm taking no credit!). I'm simply reposting it to this sticky thread since the "history" link at the beginning of this thread does not seem to work.

Q: What changes and updates have been done over the years?

A: There have been several, but most of them are easily overlooked. Thebikes get new stickers every year, and occasionally new lettering on the seat. I won't bother detailing cosmetic changes, other than noting thebikes changed from NH-196 (Ross white) in 1999 to R-134 (Fighting Red) in 2000. Frame changed colour too, from NH-262M to NH-146M (Accurate Silver Metallic). There have been quite a few country specific jettingchanges as well, and they were already covered earlier in this document.

During 1996:************The oil pump drive gear and the clutch lifter pins were updated.

In 1997:******** There are some hints that the 2nd gear upgrade happened here and notin 2000 as listed below.

In 1998:********The biggest change was the exhaust tip and the airbox inlet duct.The exhaust tip no longer had a slip in silencer part, but was insteadfixed at a 3/4" output size. The airbox duct used to be a two piece unit,and now it was all one molded chunk of rubber. The idea of both of thesechanges was to be non-removable restrictions so that they could installleaner jetting without worrying that the end user would pull out therestrictions and run the engine dangerously lean. So now you got a 52/142instead of the 62/162 for pilot/main jets. California got even leaner jets,while Europe bikes retained the 162 main. A different CDI box and flywheel were found on North American 400s thisyear. John Rushworth in his package of info seemed to think the newerCDI ignition had less advance. The different flywheel might be for thesame reason, as the placement of the little metal strip on the outside ofthe flywheel is what the CDI box uses as a reference to determine when tospark. Note that the Europe/Aus (ED/U/DK) bikes retained the original CDIbox and flywheel. I can only guess that the ignition change was in conjunction with the leaner jetting that North American bikes got. The kickstart was beefed up a bit to prevent breakage. The forks werechanged, with the spring retainer that used to go under the damperrod nut no longer being used (hence the different length springs). The airbox lid had an extra bit added to it to hold the filter retainer on once the lid was closed, as the 96/97 versions could silently eject and let the filter fall into the airbox. Shock pivots were changed fromthe older style spherical pivots to needle bearings.

In 1999:********The countershaft size was upped 1mm from 17mm to 18mm and hence somec'shaft related gears/bushings/washers needed to be changed to fit too.The kickstart spindle was also upped 2mm. The kickstart one is easy to spot.Just look at the numbers on the black oil seal around the kickstarter shaft.Newer seals are 20mm ID, (30mm OD); older ones are 18mm ID, (29mm OD). Shaft shear failures were reported (yikes!), hence these updates. If youhave a 1998 or older with a shear failure, it might be worth looking intothe machining required to accept the newer parts. It seems the new kickstart shaft meant a new kickstart lever for 1999 as well. Part way through theyear, they started using a new head gasket (12251-MBV-003).

In 2000:********Got an updated second gear set (drive and driven) in the transmission.The newer gear part numbers end in 671 and should be backwards compatiblewith older bikes. Although the information I have indicates this tookplace in 2000, there is information on the internet that seems to indicatethe 2nd gear upgrade took place as early as 1997.

I am not aware of any other changes that took place after this.

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When replacing stock handguards on either the XR2.5 or the XR4 the following list of Honda Parts are required to complete the job perfect.

1. Brake Lever Bolt - part #90114-166-006

2. Brake Lever Rubber Boot - part #53176-ML3-791

3. Clutch Lever Bolt - part #90114-428-870

4. Clutch Lever Rubber Boot - part #53177-430-000

Also you'll need 1 nut for each bolt, my dealer just gave me two with the little locking grooves cut into them.

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What kind of 2 stroke oil should I put in my XR4

Soooo do you still own the XR4?? :):)

How do you think it would have done on your GC trip??


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Hi Kev,

I just bought an 2001 xr400 and have been thinking of buying a fork brace for it! Do you have any input about the pro's and con's of fork brace's and or which is the best out there!!

Thanks in advance,

mitch the un-:thumbsup:

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Post deleted by Kev_XR

Kevin, was it you that made the "thumper" definition with urbandictionary.com?

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Xr400 Question??? I just bought a 2001 XR400. I bought the manual, adjusted the valves, cleaned oil screens ect....But how do i check that my timing chain is in good order?? I want to go through this bike top to bottom before this season really starts.

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