Gordon's Mods for XR400

[mattiasnowak]

Thanks for your reply.

While they where of the bike I decided to grind them a little bit. Now the bike is fully modded according to Gordons Mods. I opened up the ports in the head, put in a 10.1:1 piston and a CRF450 camchain before I sold it and now when i inspected it everything still looks brand new. The guy I sold the bike to didn't ride it much since he had one more XR400.

[cook81]

I'm new to Thumper Talk but wanted to say thanks for all of the great info on this site. I recently bought a 2000 XR400. Its like new. I read tons of post on here and did the Gordon / Kevin Mods. 55, 155 jets worked for me here in Dallas. I was skeptical - but WOW!

 

Race Tech suspension has been ordered.

[Edem_Alive]

Links appear to be broken

[hughiexr]

This list of modifications can be found on several websites. If you have a stock XR400 or any XR, these modifications may help.

http://groups.yahoo.com/group/xr400/files/%21%21%21%20Gordon%27s%20XR400%20Mods%20%21%21%21/GordonMods.txt

The mods are also on this site.

http://www.dirtbike.ws/node.php?id=2

As well as Gordons lesser know suspension mods, and Gordons "what to take riding"

MY MODIFICATIONS TO A 2000 MODEL HONDA XR400R

(Revised: Nov 25, 2000)

-----------------

Stock Carb Specs

-----------------

Main 142, Pilot #52, Needle Clip in 3rd groove. Right off the

showroom floor, mine ran fine, but definitely on the rich side.

Removing the airbox snorkel without re-jetting, however, made

it run lean and overheat.

-----------------------------------------------

RELIEVING THE 2000 HONDA XR400R MUFFLER BAFFLE

-----------------------------------------------

(This is a very simple procedure, and one that can be almost

as easily reversed. Best of all, though... it works.)

After carefully examining the stock baffle/spark arrestor,

and running some flow numbers for the different areas

involved with the numerous plates and baffles (both in the

muffler and on the baffle insert), I've come to the

conclusion that the primary restriction to exhaust flow is

the small final outlet, which has an i.d. (inner diameter)

of only 20mm. Without removing the baffle insert from the

muffler, examine the exhaust tip. Notice the actual outlet,

which measures 20mm i.d. (approx. 0.787"). Around this is

a larger 'bright finish' ring which appears to have no real

function, but may be to help prevent the rider from coming

into contact with the actual outlet, which probably runs

hotter. Down in between the 20mm outlet and the bright-finish

outer ring, there is room to drill 1/4" holes into the baffle

to provide additional exhaust flow area. Holes drilled in

this area will be 'inside' the spark arrestor screen, by the

way, so the spark arrestor function is maintained.

On my baffle insert, the area to be drilled is large enough

to accept a 1/4" drill, but there's a benefit to using a #2

drill bit (0.21") (or maybe a 7/32" bit) which I'll explain

a little later on.

Since the stock 20mm (0.787") outlet provides a flow area

of only 0.4862 sq.in., and a 0.21" hole has a flow area of

0.0346 sq. in., each 0.21' hole adds 7.1% more flow area.

Just three such holes will increase the exhaust flow area

by over 21%, and four will increase it by over 28%.

First I ran the engine with the undrilled baffle, to get an

up-close feel for the sound level at idle, and while revving

the engine. After drilling one hole, I could barely hear any

difference. After drilling a second hole, I could hear the

difference, but it was slight. The third hole made a bigger

difference, but still not objectionaably loud. The fourth

hole made it just a little louder than I was willing to accept,

adding a definite bark to the exhaust note. Since I had use a

#2 drill bit, which is approx 0.21" in diameter (it's supposed

to be 0.221"), I was able to plug the 4th hole very simply by

screwing in a 1/4x28 set screw, which I woudn't be able to do

had I drilled the holes with a 1/4" bit. This effectively

reverted back to having just three holes, and it also indicates

that I can plug them all with 1/4x28 set screws, to return to

the stock sound level if necessary. Come to think of it, I

guess you could say that this modification is "tunable" by

inserting or removing set-screws from numerous holes.

A brief test ride with stock jetting showed that the added three

holes gave the bike a cleaner and stronger throttle response,

probably because it runs rich when totally stock. It was now

running cleaner, so the added 21.3% flow area was beneficial,

and it had cost me nothing but a little time. It's also totally

reversible by plugging the holes with set-screws.

It is NOT necessary to remove the insert when drilling each hole.

The metal chips will fall either outside the muffler, or into the

screened area of the spark arrestor. Once you have drilled the

desired number of holes, you can then remove the insert and shake

out the tiny pieces if you so desire. If you don't, they will

eventually fly out the exhaust outlet anyway, since the spark

arrestor screen prevents them from falling down inside the main

muffler.

---------------------------------

GRINDING THE WELDED HEADER INLET

---------------------------------

I'd read about the header inlets being partially shut off by the

welding that builds up when welding the 1" i.d. header pipes to

the clamping flanges, so I examined mine. Simply loosen the

clamp bolt where the header pipes assembly slides into the

muffler, and then loosen and remove the four nuts (two per pipe)

where the headers are clamped to the head. The muffler bolt and

all four clamp nuts accept a 12mm socket. Then the header pipes

assembly slides forward and into your hands.

On mine, a 2000 model, the built-up welded area in each pipe was

terrible! The remaining opening measured a rough 0.75", leaving

a flow area of only 0.44 sq.in. A 1" i.d. pipe has a flow area

of 0.78 sq.in, so the welding left only 58% of that! I started

grinding down the built-up welds using small grinding stones in

my Dremel Moto-tool, but that was too slow. I went to the hardware

store and bought some inexpensive coarse grinding stones to fit my

3/8" drill, and one 1" ball stone for finishing. I spent over two

hours grinding away. As a "size guide", I chose an 18mm socket that

has an outer diameter of 0.944" (different brands will vary in size,

of course). Once the 18mm socket would slide into the header pipe,

I quit, not wanting to remove too much of the weld, and weaken the

joint. I then used the 1" ball grinding stone to finish up. Since

the stone itself wears away faster than the weld material, I ground

a little on each pipe, going back and forth between the two, until

enough of the stone wore away to fit into the opening. This final

touch didn't really make either opening larger, but it did make

them both about the same size and shape.

Since I started with a 0.75" opening, which had a flow area of

only 0.44 sq.in., and finished with a 0.944" opening, which has

a flow area of 0.670 sq.in., I achieved a gain of more than 52.5%.

In one afternoon I significantly improved the flow characteristics

of the stock exhaust system, and my total investment was under $10

(for some cheap grinding stones and one 1/4x28 set screw). I

already had the 3/8" electric drill and #2 drill bit.

------------------

AIR INTAKE SYSTEM

------------------

I removed the air box snorkel, and then used a scrap of aluminum

window screen to cover the opening to keep out trash and clumps

of mud. I then removed the stock air filter and support, the latter

of which includes the backfire screen. Noting that the backfire

screen consists of two layers of screen, between which are trapped

two more layers (actually a flattened screen 'tube'), I carefully

cut away only the outer layer of screen, and removed the trapped

inner piece, leaving only one, the inner layer, of the original

four-layers of screen. I happen to like foam air filters, so I'm

sticking with the stock filter for now. (I later bought a TwinAir

filter, but with the backfire screen modified, I see no performance

difference between the TwinAir and the stock air filter. If I

were using a louder and more free-flowing exhaust, perhaps the

TwinAir filter would make a difference.)

NOTE: Cutting the metal screen is a chore, and it's difficult to

get rid of every tiny little piece of wire (from the screen) you

cut, so I no longer recommend cutting the stock backfire screen.

Intsead, buy a UniFilter air filter for the XR400R. It comes

with a screenless air filter support, and a less restrictive air

filter.

Despite what I read elsewhere, it is NOT necessary to move or

remove the subframe to remove the carburetor! After removing the

seat and gas tank, I simply loosened the two clamps holding the

carb to the airbox duct and intake manifold, then loosened and

removed the three bolts holding the intake manifold to the head.

By turning the intake manifold a little CCW first, the carb and

intake manifold then slide easily out the left side. After

removing the carb from the intake manifold, I examined the

composite rubber & plastic intake manifold. I do not think it

was necessary, nor do I think I gained anything from it, but

I used my Dremel Moto-tool with a medium size sanding drum to

clean up the few ridges found inside. Just couldn't resist!

-------------------------

JETTING CHANGES REQUIRED

-------------------------

After two days of trial and error jetting (and a few hours more

since then), I came to find that the exact same jetting recommended

by CYCLE NEWS (several years ago) worked best. I'm using a 160 main

jet, a #60 pilot jet, and the triple-tapered carb needle that comes

standard in the 1998 and later XR400R's, with the needle clip in the

stock (3rd groove) position. My altitude is approx 700' above sea

level, and I ride regularly up to 3200', where it still seems to

work just fine. I've also replaced the 15t drive sprocket with a 14t.

For the terrain where I ride, the stock gearing is a bit too high.

Depending on your particular machine, you might prefer a 158 main

jet is using a stock or modified stock exhaust. If using a louder

and nmore free flowing exhaust pipe, or the 1996-97 spark arrestor

without the muffler insert, you'll want to use either a 160 or 162

main jet.

--------

RESULTS

--------

How my XR400R might compare to a differently modified version, I

don't know. All I do know is that it easily pulls away from an

unmodified 1999 model, and that I am able to pull up the front

wheel at will in any of the first 3 gears. It is a little louder

than stock, but not as loud as a KLX300 with its muffler tip

removed, and it is nowhere near as loud as an XR or WR 400 with

the muffler insert removed altogether. It's more than I need for

woods riding, but without being 'difficult' to ride.

-----------------------------------

XR400R Spark Arrestor/Muffler Note

-----------------------------------

The 1996/97 XR400R has a two-piece exhaust pipe insert. The

removable spark arrestor has a removable muffler insert. With the

muffler insert in place, the exhaust is very quiet and very

restricted. With the muffler insert removed, the spark arrestor

alone has an open outlet nearly 1.5" in diameter, so it makes

really good power, but is also pretty loud. The 1998/01 spark

arrestor insert has the small 0.787" outlet which serves as the

combined spark arrestor and muffler, all in one piece. It has more

restriction than the 1996/97 spark arrestor alone, but more

restriction than the 1996/97 spark arrestor with the muffler insert.

Both of the two different spark arrestors fit all years of the

XR400R's exhaust pipe (three small bolts).

Gordon Banks

Huntsville, AL

glbanks@b...

 

probs one of the best tips so far

[Kev_XR]

probs one of the best tips so far

Gordon did us a huge favor.

In hindsight, it is all pretty simple.

The 96-97 XR400R was shipped, assuming the intake and exhaust rest rectors would be removed for racing.

The 98-04 XR400R was shipped assuming the restrictions would be left in place.

Gordon's mods just turns the restricted xr400 back into the unrestricted version.

When you are done, the jetting should be similar to the 96-97. Different needle and slide, of course.

PS. I don't think the welds in the header were due to Honda getting sloppy, I think they were to create more back pressure to fit the restricted set up.

[1304]

Can someone tell what settings and jets I need for my 2003 xr250r after I've removed the snorkel and spark arrester

[Firestone]

Can someone tell what settings and jets I need for my 2003 xr250r after I've removed the snorkel and spark arrester

 

Try one richer jet pilot and main. 

[BFMDan]

Question about the baffle . . . I have a 2004 XR250.

I was able to take the entire baffle out via three 10mm bolts. Now the tail pipe is simply wide open. This seems different that everyone else's experiences.

Anyone care to offer advice or suggestions?

 

HB

 

[Trailryder42]

You didn't say what you're wanting to accomplish, but see that bolt in the side, picture #2. If I'm not mistaken, removing that should allow the center section to come out. A lot of 250 riders just run the outer silver trim ring with intact spark arrestor.

[BFMDan]

11 hours ago, Trailryder42 said:

You didn't say what you're wanting to accomplish, but see that bolt in the side, picture #2. If I'm not mistaken, removing that should allow the center section to come out. A lot of 250 riders just run the outer silver trim ring with intact spark arrestor.

Aha! I see. I hadn't even noticed that bolt on the side. (blushing, just a bit). Thanks for pointing that out to me - Haha!

As for what I'm wanting to accomplish - well, I was just trying to start some of these "Godon's Mods". So, I thought I'd jump into the "remove the baffle" suggestion.

 

HB

[Trailryder42]

Yeah, you wouldn't want to run an open exhaust with no baffle. And you don't to do anything that compromises the integrity of the spark arrestor. For the XR400, drilling the holes in the recommended place, and for the XR250, unlike the 400, that inner piece inside the silver trim ring is removable, so that's what 250 riders do. Both mods provide more exhaust flow but keep the integrity of the arrestor intact.

[BFMDan]

On 6/25/2017 at 9:38 PM, Trailryder42 said:

You didn't say what you're wanting to accomplish, but see that bolt in the side, picture #2. If I'm not mistaken, removing that should allow the center section to come out. A lot of 250 riders just run the outer silver trim ring with intact spark arrestor.

Hmmm, I removed the bolt (picture #2 in my original post) but the baffle won't come loose/out. I tried prying, pulling, etc. but couldn't get it to budge. Now, I didn't want to bend the spark arrestor screen - damage the silver ring - bend the baffle or anything like that, so, I did not use herculean efforts . . . but, I did try pretty hard. I also couldn't see how to remove the spark arrestor screen . . . so there was no way to gently tap out (say, with a rubber mallet) the arrestor from the back side. Is there a spot weld or something deep up there inside the silver ring of which I'm unawares?

 

HB

Edited June 27, 2017 by Haybails

[Trailryder42]

Sorry man, I can't remember exactly what it takes to get it apart. Ask in the regular XR250/400 forum. I know there are guys in there that can probably tell you. This thread is kinda dead.

And I may remembering a different exhaust, but it may require taking a hole saw to it and cutting out the small center exit pipe. My friends tell me I have CRS syndrome.

 

Edited June 27, 2017 by Trailryder42

[BFMDan]

2 hours ago, Trailryder42 said:

Sorry man, I can't remember exactly what it takes to get it apart. Ask in the regular XR250/400 forum. I know there are guys in there that can probably tell you. This thread is kinda dead.

And I may remembering a different exhaust, but it may require taking a hole saw to it and cutting out the small center exit pipe. My friends tell me I have CRS syndrome.

 

Ah Ha! Good information here:

Thumper Talk discussion on XR250 Baffle removal

4Strokes.com article (with pictures) of XR250 Baffle removal

Thank you for your input, though.

 

HB

[Romy]

please delete post, wrong place

Edited March 5, 2018 by Romy
post somehow ended up in wrong thread

[hibobb]

I need some advice,

I just joined thumpertalk to ask you guys a question on a 2002 XR400R I just picked up. It was originally a california bike. I am in Wisconsin at maybe 500 foot altitude. I have tried the Gordon mods (with the correct jets), and also went back to stock (with the other correct jets) I do have the A16 non-california needle and seat back in it. I can start it fine, it runs great, but there is always a stumble/bog/stutter when I wack the throttle off of idle, like for wheeling over a log. Rolling on the throttle is great, the front end flys up, it just when twist too fast that I have an issue.

142 main and 52 pilot when stock, 158 main and 58 pilot when gordon mods, have the A16 needle and seat, always adjusting the fuel screw, the carb has been cleaned three times now, ultrasonic and with carb dip. Sprayed carb cleaner thru all ports, watched the spray shoot into carb throat. Exhaust screen is clean. New stock air filter and new UNI air filter, snorkel on and snorkel off, exhaust tip drilled and exhaust tip stock. Valves adjusted to 0.004 & 0.005. Idle speed 1,300 (guesstimate)

My history has been either two-strokes or four stroke dual sports with CV style carbs. I am starting to think the CV carb opened slower (due to their design) and I didn't have the loss of vacuum that is affecting the XR400 carburetor. Short of replacing the stock carb with a pumper one, am I just gonna have to get used to rolling on the throttle a little more gradual? 

Thanks, Bob

[Trailryder42]

Welcome to the forum Bob.

First off, the A16 needle you have IS the CA. needle. The 49 state needle is the A16A. Stock clip position is 3rd from top.

For 500' elevation and full Gordo mods, 158/58 jetting may not be enough. Something to consider.

It can be difficult to completely eliminate the off idle hesitation when whacking the throttle open quickly with the stock carb, but with careful tuning it can be minimized. How the engine responds to throttle inputs like that sitting on a stand at idle compared to during riding when you may be running down the trail in gear or coasting under engine braking, is going to be different.

Make sure you remove the fuel screw and clean that passage during your cleaning. Verify its parts are all there and installed in correct order and that the oring is in good shape. Be sure the intake manifold oring is in good shape. The bike being new to you, I'd replace these two orings for your own baseline status and because they're probably still original. You don't want to be chasing jetting problems with questionable orings and possible air leaks.

Verify your float level is set to spec. of 14.5mm. And altho not part of the Gordo mods, I suggest setting the max drop tang on the float so the float has a max drop of 19.5mm. You'll find that it's around 25mm stock. Doesn't need to be that much. Can cause a stumble on G-outs and such.

 

Edited October 24, 2018 by Trailryder42

[hibobb]

T/R,

Thanks for the quick reply. I looked at the needle I took out, it was stamped "A2EA" I am pretty sure that was the california one. The package for the one I ordered and put it said "16012-KCY-681" but that was the set, with the seat, clip, & needle. To the best of my knowledge, I had ordered it correctly. Will look again when I open the carb up.

I have a new o-ring on the fuel screw, as it was missing when I got the bike. O-ring, Washer, Spring, Screw installed in correct order. Each time I took the carb apart, I took ALL the jets (and screw) out, and verified the passages were clean & open, same it the jets. I took a gage pin thru the jets to verify the size of the opening. checked the emulsion tube, all those holes were clear. O-ring on manifold looks perfect. New gas without ethanol being used.

I am starting to understand that without a pumper carb, I can't just wack the throttle and wheelie off into the sunset. At the starting line to a race, no one is sitting at idle for a reason. The bike idles fine, starts fine, runs fine... I should stop being so anal. I am an old toad at the twilight of my riding days, I should just go out and have fun...

I will address the float level as you suggest. I had checked, and it was within the range of the service manual, but maybe less is better.

Thanks again, Bob

Edited October 25, 2018 by hibobb

[Trailryder42]

8 minutes ago, hibobb said:

I will address the float level as you suggest. I had checked, and it was within the range of the service manual, but maybe less is better.

14.5mm is the standard minimum drop spec given in the manual. That's the floats highest point. The maximum drop is how much the float would drop if the bowl was empty or when you hit a g-out, jump, ect. that forces the float downward. Limiting that sudden downward travel prevents an engine stumble.

I agree, get the off idle throttle response set as good as you can and just ride the thing.

[cmbthumper]

^^

I just got these upgrades for my carb clean/rebuild/jetting. If i learned correctly from my thousand questions to Trailryder42, the 681 is the triple tapered needle. Hard to tell from the pic but it does go from small at the tip to medium in the center and then clip size so i assume it is the triple taper.

 

Edited October 25, 2018 by cmbthumper