THROW THAT STOCK XR CARB IN THE TRASH!!!!
BACK IN 1985 a stock XR 350R put out 26 hp. Today, 15 years later (because of emission laws in CA) a stock XR 400R only puts out about 28. No offense, but the stock XR 400 is a total wimp. I couldn't believe how gutless it was for $5700 worth of bike. But wa-hey! I live in California and it passes smog! Know that if you have a CA XR400 things are a little different. What I mean is A LOT LEANER!!!
My bike was so lean you'd have to run it with the choke for what seemed like forever! It drove me insane. And what about that little glitch off the bottom that XR's are so notorious for? You got it! That was there as well! Worse than ever!
I toyed with the stock carb for days. Dicking around with jetting and float levels and going crazy in the process. Then one day I came up with an absolutely moronic idea!
UPDATE: Some people will tell you that the stock carb can be jetted to work great. This is partially true. The real question here is: Great compared to what? I can tell you from personal experience that it is only great compared to stock jetting (which if you bought your bike in CA is a joke!). As you'll see in a few paragraphs there is no comparison to the IDEAL AFTERMARKET CARB which I later discovered!
HEY! LET'S PUT AN AMERICAN MADE CARB ON A JAPANESE BIKE! (bad decision bucko…)
Close to $300 and a few headaches later I realized the EDELBROCK QUICKSILVER CARB has no business being on an XR!!!!! If anyone wants a great deal on a brand new quicksilver carb for their XR 400 just email me. It's brand new in the box. Less than 2 hours use! Paid $300 will sell for $99! There are a handful of guy out there that swear by these things but I don't believe any of them have used the carb I tried next…
What was I thinking?
(oh? I wasn't!)
That night in total frustration I made a phone call to my friend Tim who I used to ride XR's with (he has since defected and bought a YZ400!). Tim told me a story that changed my life forever. He shared with me that on his Dads 97 XR400 they installed a Mikuni Pumper carb. Tim tweeked with the jetting and pumper set up for a day (he's a jetting master) and said that his dad's 400 had been completely transformed! He guessed it was an immediate bolt on 5 hp increase! He said it even felt a little like his YZ400 in the mid range! The change was so dramatic he called it the single best mod anyone could do to an XR 400… Remember, this is coming from a past and current XR buff!
The next morning I was on the phone to Steve Avigliano at XR's Only since they had the best price on the carb. Tim's dad paid close to $425 and XR's only had them for only $370 delivered. Better yet the carb was all set up for my bike. The next day the carb came and I installed it in about 30 minutes.
UPDATE: If you order a Mikuni Pumper from XR's only and ask for Steve Avigliano tell him you know me and demand that he sell it to you for $350 delivered or you'll go elsewhere! He owes me one!
When I fired the bike up and cracked the throttle it felt crisp and I knew this was going to be good! Stock jetting in the pumper was 125 main and 12.5 pilot.
IMPORTANT NOTE: please keep in mind that I did have my final aftermarket exhaust on the bike as well).
I took off out of the driveway and literally went flying around the neighborhood. I couldn't believe how much more power the bike had! It felt like an XR on nitrous! With the stock bike I couldn't pull wheelies without the clutch on flat pavement in fourth gear. With the pumper carb I could jack it up in every gear without the clutch! People don't believe me when I tell them this! When I got off the back that night I called my 2 friends who both had 99 400's and said "It's unbelievable! I can pull wheelies without the clutch in every gear!". They didn't believe me for even a minute so I told them to come over and I'd show them in front of the house. I showed them and then let them each ride the bike…
The next day they called Steve at XR's Only and
ordered the Mikuni Pumper Carb as well! This carb is "THE CARB" for
the XR 400. It literally tranforms the bike into real thumper that
can actually tackle real hill and terrain… I even talked with
extensively with Freddy the owner of XR's only and he agreed it's every
bit as good as the $500 Keihin carb that comes on the YZ and WR 400's and
I believe him since he's ran both!
JETTING THE MIKUNI PUMPER
If you buy the pumper from XR's Only it will come set up perfect or almost perfect for your altitude. Again, people flip on the jetting I run but it's what works for me and my style. Remember, my type of riding I'm chugging the bike a lot and making the most usable power I can, primarily operating in the low end and mid range and top end occasionally when the terrain opens up. Also, realize that I run an aftermarket exhaust, air filter and have the snorkel removed from my air box under the seat to let it breathe all it can (more on this later). With that said this is the jetting I run for 3,000 to 6,000 feet:
17.5 Pilot - 125 Main
If you don't buy the Pumper Carb from XR's only the jetting may be wrong but more importantly the PUMPER ACTUATION definitely will! The pumper mechanism (stock) on the mikuni comes on way too early. Set it up to come on at about 1/3 rd throttle. This is a big trick with the Mikuni. Most people will run a leaner pilot and have the pumper mechanism come on early when what we've found works best is to go rich on the the pilot and have the pumper mechanism come on as late as half throttle!
An XR without that bottom end off idle glitch is a wonderful experience…
The other thing I should point out is that Mikuni
makes an aftermarket needle for the carb which I use as well. It's
a dual taper needle that leans out the mid range to make it a little crisper.
When you first run the needle you'll notice a lot of popping in the exhaust
when you let off the gas. Just richen up the air screw to get rid
of this. I run the needle in the standard/recommended position with
the air screw about 3" turns out. The needle is worth the $28.00
and is also available from XR's only as well.
WHAT ABOUT THAT LITTLE OFF IDLE GLITCH?
Gone! Completely gone! I attribute this to the 17.5 Pilot. When I told Steve at XR's Only about my experience with the 17.5 pilot he couldn't believe it! He said "We've never gone bigger than a 15.0 in any of our bikes, even our 440 with a cam and porting!". I asked him "Have you ever tried it?" No… He replied. The mechanic that works on my bike said it was the most impressive 400 he ever rode and he has ridden a lot of them! When going up in altitude I drop the a size on the main but leave the pilot the same and toy with the air screw. Remember, this jetting is for 3,000 to 6,000 feet.
(IMPORTANT NOTE!!!! IF YOU RUN A
STOCK MOTOR WITH THIS CARB AND RIDE THE SAME ELEVATION 3 to 6K+ YOU WILL
WANT TO RUN THE FOLLOWING JETTING 15 Pilot - 125 Main. As you will see,
there are some other things I did to my motor that make the richer jetting
work...)
THE LOW DOWN ON AFTERMARKET EXHAUST
First let me cover air filters (real quick I promise!). I ran the stock filter for a while and then felt the need to change it for more breathing room. Went to a uni-filter and never liked the way it fit. Didn't really notice any difference in breathing either. Stayed away from K & N's because they seemed to have a bad rap even though I don't ride in water much. I pulled a 180 on this one day when I ran into a major XR 600 buff whose lived in town his whole life. This was a guy that used to ride a dual shock XR 500 back when I was on my BMX bike! Long story short, I asked him about K & N's and he swore by them! Ran them on all his XR's for the last 20 years. Needless to say I put a K & N on the next day and was a believer! The K & N breathed a lot better as I had to adjust the air screw to compensate. Noticed a little crisper power all the way throughout.
UPDATE: Obviously I recommend K & N filters as well.
I will say that I Run a little more oil on mine than most. If you
do ride in a lot of water you can still run a K&N, just make sure to
use the FILTER SKINS over it.
NOW LET'S TALK EXHAUST!
When it came to exhaust I was looking for low noise levels with maximum
power increases in the low end and mid range with NO SACRIFICE in top end.
It's easy to gain power in the top end with an exhaust; just open it up.
Increasing the low and mid without losing the top is a little different
because it has to do with manipulating back pressure. You need
to maintain good back pressure at low and mid rpm but at the same time
have great flow to LET IT RIP on top.
WHITE BROS E-SERIES
The complete White Bros E-Series was good but was too F!!!! loud and
because of the fat header lost the bottom end.
XR's ONLY COMPETITION EXHAUST
The XR's Only exhaust (with 12 discs) looked Killer and made the exact
type of power I wanted but was Also too loud for my needs.
COMPLETE BIG GUN SYSTEM (With Spark Arrestor/Quiet Core!)
BIG GUN has a really bad rap for being a noisy pipe but what no one
realizes is that they make a "SPARK ARRESTOR/QUIET CORE" option ($97.00)
which
fits inside their racing series exhaust. This lowers it down
below 100 decibels and the power delivery is awesome! A bolstered
bottom end and mid range with no sacrifice in top end. In super rocky/slippery
areas where I would really dawg the bike and it would come off the pipe
(with stock exhaust) the BIG GUN would just makes GOBS of usable and tractable
power.
The side benefit of the big gun is that it has a very low and deep sound to it as opposed to other exhaust systems, making it even less irritating to the ears. Too me it is the most bitchin sounding exhaust on an XR! In fact, white bros is now selling BIG GUN as it slowly catches on with the XR crowd.
I went with the complete BIG GUN system. The header pipe is by no means MASSIVE but there is a reason for this which will be explained in the literature. This system is expensive. A lot of these mods are expensive. I saved a lot of money by group purchasing this stuff and avoiding sales tax. For example. When it came to the exhaust; rather than paying well over $500 dealing directly with BIG GUN or a dealer in my state (7.75% sales tax) I called a guy named Jeff at
And wheeled and dealed, ordering two systems with a 15% discount, no shipping and no sales tax. I recommend you do the same with all your mods. Think before you pick up the phone.
One last thing, since I like my bike plain Jane. The BIG GUN exhaust looks just a like a two stroke exhaust (only bigger) and has a BIG GUN emblem on the silencer – RIVETED ON!!! I cut the rivets, removed the emblem and out new rivets to fill the holes!!!
NOTE: I recently heard that in 4 stroke dirt bike they tested over a dozen pipes and the BIG GUN and XR's Only pipe we're the top two.
UPDATE: I believe the BIG GUN COMPLETE SYSTEM WITH SPARK ARRESTOR/QUIET
CORE is the best exhaust for the XR 400. However, if you ride the
bike and wide open or nearly wide open throttle for extended periods I
have heard the silencers can have problems keeping the packing in.
This dilemma may be fixed as there is more durable packing available now.
If this is your riding situation I would check with PAUL at BIG GUN for
details before ordering.
NOTE ON PACKING THE BIG GUN
The BIG GUN exhaust looks just like a 2 stroke exhaust, only bigger.
It has a silencer which needs to be packed. Please be aware that
a loosely packed silencer will sound deeper and quieter than a tightly
packed one. This is contrary to the popular belief that a tightly
hard packed silencer is quieter than a looser one. I packed my silencer
moderately tight.
******************************************************
10/12/00 IMPORTANT UPDATE!!!!!
******************************************************
<Get Ready For A Paradigm Shift>
In an effort to make my bike quieter I later (after ALL mods were done) put my stock exhaust back on. Believe it or not but it makes GOBS more torque and is quiet to boot (giving me even more riding opportunities). In the low and the mid in pulls like a 600. No joke! It did lose a little on the very top but gain, remember the kind of riding I like to do. I quickly remedied the minor loss by getting a "VORTIP" from
The "VORTIP" is an aftermarket baffle that keeps the noise down to 92 decibels but opens up the flow on top a little more.
THE VERDICT! YOU WON'T BELIEVE THIS!!!
I am now convinced that aftermarket exhaust is a TOTAL SCAM... (for the 400 anyway) These companies charge us up to $500 for a complete exhaust and all we're getting is a little more horsepower at the expense of vital torque! As for the weight loss, it's less than 2 pounds on a 250lb bike. What a rip off!
Have you ever wondered why magazines always show horsepower ratings
on aftermarket exhaust but NEVER show you torque? Hmmm.....
I recently had an interested conversation with Scott Summers about this.
ODDS AND ENDS BEFORE DROPPINGTHE BIG BUCKS AND GOING BROKE!
XR's Only makes a lot of cool stuff for XR's. Here are some other odds and ends I purchased for my bike. XR's Only tool bag that mounts to the stock fender through the stock fender bolts. XR's Only oil dip stick with Temp Guage display (way cool! Just make sure you put a little oil on the ring that holds the glass inspection window on so it won't rust!) XR's Only aluminum shark fin disc guard protector!
UPDATE: As of this writing they are working on a new disc guard that mounts through the axle (totally trick look but $130. Ouch!).
DEVOL full protection aluminum front disc guard. (that acerbis plastic
is a joke! I bent my disc and paid a guy $20 to true it!) XR's Only
magnetic oil drain bolt.
HOW TO FLIP OUT GUYS ON YZ 400's and ATK 605's!!!
The XR is a green sticker legal bike. This means it has to adhere
to strict emission regulations and this goes way beyond the carburetor,
intake and exhaust. It has to do with the valve timing and cam as
well. This is why red sticker bikes like the YZ 400 can put out a
strong 40+ hp out of the crate. Although the YZ 400 has no bottom
end and a long wheelbase making it virtually worthless on slippery technical
trails, it will always take off like a bat out of hell next to an XR on
an open straight. The YZ 400 is like a 4 stroke with 2 stroke power
delivery. If you've never ridden one it is rather entertaining.
If you ride desert, you'll love it! (note: I was originally going
to buy a WR instead of an XR until I rode one but this is another story).