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Gordon's Mods for XR400


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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...

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  • 1 year later...

I have not tested how loud drilling the pipe makes the bike.

Gordons Mods was done before the new 96db sound laws were enacted.

If you only pull the intake snorkle and switch to a UniFilter with the high flow cage, Motocross Action states you should use a 55 pilot and 155 main jet. If your bike is not a California bike, you already have an A16A needle in the 3rd clip stock.

With a little testing, you might go up to 58 and 158 jets. I have pulled the 96 spark arrestor / Baja Designs Vortip baffle and replaced it with the stock 98-03 baffle. The bike ran a bit stuffed up (rich) with a 58 pilot and 162 main jet. The power difference wasn't huge.

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First of all, ye Californians must know, not everybody is being persecuted or harassed about noise. Out east here we enjoy alittle more freedom, and a little less high stepping than there on the left coast.

With that said, I would bet that a Gordon Modded exhaust would be dog-gone close to the CA. present levels of noise acceptability.

Also there have been those on this board who claim that a "96" BajaDesigns end cap/SA with the Baja baffle falls below the 96db limit. This, I believe is the best compromise in performance/noise.

I have pulled the 96 spark arrestor / Baja Designs Vortip baffle and replaced it with the stock 98-03 baffle. The bike ran a bit stuffed up (rich) with a 58 pilot and 162 main jet. The power difference wasn't huge.

This is counter productive to everything done upstream of the end of the exhaust. I would question this finding, specifically "The power difference wasn't huge."

The "Gordon's mods" are beneficial to performance as a whole, to achieve the full benefit, all mods must be performed as a group, including addressing the stuffy stock baffle.

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Drilling "only the 3 holes" suggested by Gordon only slightly increases exhaust noise. It is not obnoxious at all. Removing the baffle/arrrestor completely, now THAT would be. If you have removed the snorkle already and rejetted then you do need to do "something" with the exhaust. Will most likely have to rejet again when you mod the exhaust, to dial it in. Trying to get it dialed in with the just the Snorkle removed and UNI filter can be problematic at best. IMO

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My 60/160 jetting + needle at 4th clip from top is slightly richer than most suggest. Opening up the exhaust a little might lean it out just enough (I hope). I did find a 96 pipe locally for $50. Would that be better to work with than my stock '01 pipe drilled?

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I recently removed the snorkle on my '04 XR400 and opened up the exhaust. However, instead of the 3 to 4 1/4" holes, I opted for 12 1/8 inch holes. The primary reason was that there wasn't enough room between the outlet and the beauty ring - the outlet tapers down towards the end and I didn't see any way to cleanly drill larger holes and still be able to plug them up with set screws if necessary. It's a little louder than stock - just right in my opinion.

I re-jetted to 60 / 160 - the results are impressive. I left the needle alone, but may richen it up slightly the next time I ride.

Rick

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I have tried both ways on my 01 XR4,the 1/4" drilled holes in stock one piece baffel and now have the earley model skark arrester with a Baja-Baffel insert, this combo. is far better at only 89 db. If you look at the two side by side there is a big difference in the screen area on the earley model, much more free flowing. I think it's worth the extra money for this set-up 🙂

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To address your questions.

First of all, ye Californians must know, not everybody is being persecuted or harassed about noise. Out east here we enjoy alittle more freedom, and a little less high stepping than there on the left coast.

While California is noted for it's 96db limit, all AMA off-road events and the National Forest Service require the same 96db exhaust limit. It isn't just a California thing.

With that said, I would bet that a Gordon Modded exhaust would be dog-gone close to the CA. present levels of noise acceptability.

I have no idea how loud the Gordon's mod exhuast mod with 3 holes drilled, so I can't say, "Drill away" and know there won't be a problem. I do know that my Baja Designs Vortip Baffle tests around 93db when tested by local rangers.

This is counter productive to everything done upstream of the end of the exhaust. I would question this finding, specifically "The power difference wasn't huge."

I found the difference between using the standard 98 insert and the vortip not to be huge. Try it yourself.

The "Gordon's mods" are beneficial to performance as a whole, to achieve the full benefit, all mods must be performed as a group, including addressing the stuffy stock baffle.

Not really, I have done each of the Gordon's Mods one at a time. The biggest difference is removing the intake snorkle, switching the filter cage, and rejeting from the ultra lean stock jetting.

It is possible that I use the low end of the RPM range and I don't make the XR400 engine scream, so I didn't notice the difference. Also, my observations were on a couple of rides and did not include dyno testing.

I continue to run the Baja Vortip as I do believe it does help with power, but IMHO it is not a day and night difference from stock. If I were to do it again, I would be tempted to drill a couple of holes in the stock unit. One day I just might do it to see how it changes things.

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While California is noted for it's 96db limit, all AMA off-road events and the National Forest Service require the same 96db exhaust limit. It isn't just a California thing.

Kevin,

I believe what your saying but I'm telling you I have never been tested at The Nat'l Forests nor have I ever seen anyone tested or heard of anyone being tested here. The priorities of the rangers here are different than the ones out there, here they mostly just want to know if we're having a good time. Someday I'm sure they'll get around to it but when they do all those CRF's and YZF's will keep them busy for a long time.

Back a couple posts Djlxr400 has a test result for the BajaDesigns "96" endcap w/Baja Baffle at 89db, this just might be the answer for those looking to boost performance while staying under the noise radar.

I don't think any one mod will produce a night and day difference although collectively they do provide enough reward to warrant the time and effort spent.

The mods that you said made the biggest difference consisted of 3/5ths of the "Gordon's mods".

I would never suggest that anyone pursue the "Gordon's mods" without addressing the exhaust side, the other 2/5ths.

Also, I didn't need a dyno to tell me what difference it made on my bike, just one ride and I knew.

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The point I was trying to make is that you don't have to change the exhaust. Some people don't want to bother with an aftermarket exhaust or drilling the stock exhaust. There is a good gain from the 3/5ths of the Gordon's Mods.

Of course you get more power when you open up both ends, but just opening up the intake and fixing the lean jetting helps.

This was a puzzle I was researching back in the summer of 1999. The Honda XR400 Competition manual was written for the 96-97 jetting and didn't address how to jet for the new non-removable exhaust baffle. Motocross Action magazine recommended using a 55 pilot and 155 main with a UniFilter. I switched to that combo and ran it for a while.

Later, I purchased the 96 spark arrestor and Baja Baffle, then rejetted to a 58 pilot and 162 main. Later, I bumped up to a 60 pilot.

I have done all of the Gordon's mods one at a time, so I have a fairly good feeling for how much each contributes to the whole effect. Actually, the last one I did was grinding out the headers. I left a fair amount of material as I didn't want the header to crack. I still think Honda intentionally made those welds thicker to create backpressure and they were not just sloppy welds. Honda just doesn't do welds that sloppy. Also, when a local mechanic talked with Honda Racing about hopping up an XR400, he was told to use the 96 header as it had a larger opening than the 98 header. Since the outside is the same on the 96-04 headers, I suspect the weld inside the header is what was being described and it was purposely restricted.

Some people say there is a huge difference between the stock 98 exhaust and the Baja Baffle. Others say there is little or no difference.

One day, I'll have to pull out my drill, stock exhaust baffle and DB meter to check how much louder the bike becomes with 3 1/4" holes drilled in it.

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  • 6 months later...

Make sure your bit is sharp and it will be no problem.

As for the noise levels with a modified silencer, I have the 2000 XR400 with the stock exhaust and three 1/4" holes in the end and I had mine tested by the BLM at 92db. Not bad at all. 👍

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I used a brand new bit and it doesn't seem to work. My bike is a 2000 also. I have rejetted it and pulled out the snorkel, which really helped. I'm sure that drilling out the exhuast will be good too, but I don't know what is up. Anyway, I'll figure it out, thanks for the input.

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  • 2 weeks later...

some pics would be a nice addition to this thread. us new guys need our hands held as we start cutting and grinding on our new babys.

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If you're having problems drilling, try using a small bit first (very small) then switch to the larger bit. Many times a larger bit has as hard time biting (no pun intended) into the metal. A smaller pilot hole will help a lot.

Dale - Buying a range of jets today for Saturday's tuning adventure. 👍

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  • 5 weeks later...

I have a 96 XR250R that I have recently purchased. I would like to perform some of these mods but not sure which have been done. The bike has a SuperTrap slip on but it does not look like anything has been done to the airbox. How can I tell if it has been rejetted and what is this snorkle that you are referring to. I am wanting some more power from the bike and considering the 280 mod for a winter project. Any feedback would be great.

Also, has anyone replaced the rear drum brake for a disc setup and if so, how difficult was it.

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