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XR400R need more power, please help

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Hi Guys, i have used the search button and read almost every post about "more power" in the xr400r.

i had a xr650r before with edelbrock and big-gun with airbox mod, and it ran fine :cry:

but i swapped to a xr400r because i tend to ride more in the woods. and i don’t regret it. :cry:

i like the smoothness of the bikes power when im riding in difficult situations, but when i get to open ground i would like to have more power in the bike. :cry:

i plan to have the bike for a long time so i don’t want to squeeze the juice out of it yet.

i have been reading about big-bore 415cc,416cc,426cc,430cc and 440cc, and high compression pistons.

When i read the post about 11:1 pistons and higher compression, nearly all says that you have to run it on race gas, is this necessary?, in sweden(where i live) we have 98 octane in the ordinary pumps.

my xr400r is a 2004 model and have about 500km on it, I have done all the Gordon mods on it.

i plan do buy either a mikuni pumper carb or the edelbrock pumper carb,and a 10:5-10:8 piston.

Should i bore it to a 415cc-426cc or should i just go with the stock bore and buy a high compression piston?

will i notice a difference if i bore it to 415cc-426cc?

I am looking for more low-mid power, not high rev power

Also is there some cam that will make more low-mid power?

Should I go with a Wiseco or a JE Piston?

i dont plan to buy an aftermarket exhaust, because of the increase in noise.

Thanx in advance guys :cry:, im pretty new to this with high comp pistons and big-bore

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I'm picking my 426 bore up today or tomorrow, then I have to put it back together. I'm getting 11:1 compression, which will run fine on pump gas. Also, the highest pump gas we have around here is 91 :cry: so with 98 you can run anything. Heck, my neighbors WR250 (13:1 or something) runs on pump gas.

I'll be posting once I get it all ready to go. From what I've read though, it makes a huge improvement (+5 or more horsepower?)

If you get an aftermarket pipe, get an FMF Q. Probably the same sound level as your bike without the baffle. My PowercoreIV with a silencer in it was 88db.

Other options are a cam, and.. er.. as far as I know thats about it.

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I've recently put a 11:1 426 kit with a cam and a valve job in my bike and let me tell you, it makes a huge difference. The pumper carb that I put on about 2 years ago doesn't even compare to the gains that the big bore kit makes.

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call rob barnum at barnums pro products he works magic with the xr400 he did my 416 kit and cam and valves with a pumper carb the power was awesome :cry: stopped me from buying a crf 450 :cry:

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Ok, so a 10:5-11:1 piston shouldn’t be a problem, why should i big-bore the cylinder 15-26cc? do the 15-26cc make any difference,?

Why do you do the valve job?, is it because its worn or something? Do I need to do it or buy new ones?

is there any difference between the JE piston and the Wiseco Piston, the JE piston is more expensive

Thanx guys!

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I got the 426 kit on and it made a huge differnce. I also have a pipe and airfilter so that helps a little bit too. I run 89 in mine without a problem. Couldnt tell the differnce between 89 and 92 except the price. I also did a valve job. I did this because the motor was already open. I put new seals and shims in and I also relapped the valves. I needed a new cam chain so I put that in also.

Now my bike aint not xr650r but I can stay pretty close to my brother on his 650r in drags considering the less wheel spin mine makes than his. By the way this is in sand and he beats me by 3-4 bikes lenghts. I bet my bike could hold its own against a 250 two smoker. I would get the 426 kit and maybe a hottcam stage 2.

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Unless you are an engine guru, I would hesitate at just adding a high-compression piston and not making any other engine mods. Everything in your engine has to work together, in sync. Get a copy of The Sportbike Performance Handbook by Kevin Cameron, who is an engine guru, to see what I mean.

I see lots of posts on other boards where someone buys a new bike, like a VFR, and then gets a free-flowing pipe and a K&N filter and does a snorklectomy to "let it breathe." Shortly after that, they post that their bike is hard to start, is running hot, and bogs or surges. Hmmm. Could it be that the bike is now running way more lean, because you're pumping in (and out) more air but haven't changed the fuel map? Yep, so then they have to buy a Power Commander for $300, and their fuel mileage goes to pot. Great!

If you want to tweak your bike, I'd follow the advice of the guys here who have had the bike for a while and know what gives you the most bang for the buck. Usually your money is best spent on: (a) safety gear, (:cry: lessons, © suspension, (d) jetting, and last (e) engine mods. If you're determined to do engine mods first, then the best bang for the buck is probably (a) sprocket change, (:cry: jetting/air filter, © pipe, and last (d) big bore/cam/porting/flat slide carb. I wouldn't fiddle with just the piston in a well-tuned and good running engine. But that's just me. Larry

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I have the 440 on my bike and it gives a huge increase in power to the bike. If the engine is still running strong I would hesitate with a bore kit until you start to lose compression. Also I'm getting a Hotcam Stage 1 this week. Its suppossed to give quite a bit in the low to mid range.

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Like tahoemoto said, wait till you lose compression before you do motorwork. Thats why I did mine. Freshing up a bit. So how was your xr650r with a pumper carb on it? Brother is thinking about getting something for his bike. He also is letting me pic anything out of Rockymountain and is paying for it for my birthday. :cry:

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Best way to get more power out of your XR400 is to take that turd and trade it in on a KTM or any high performance 4 stroke. XR's are great reliable bikes but lets face it your riding a 10+ year old bike when you buy it new. Let the old XR's fade into history and get them out of my way!!!! :cry:

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Colorado:im not an engine guru :cry:, I was trying to copy the HRC kit for the xr400r

and the HRC kit doesn’t big-bore the cylinder, I have done all the gordons mod on the xr400r

and change to a 14 sprocket, i got all the expensive safety gear that one should have, the only thing that’s missing is the suspension job and a skid plate.

i knew what i was buying when i got the xr400r, i didn’t want the crf450.

maybe i skip the engine mod until next year, and buy a nice carb for the xr400r this winter, and do the suspension job,

but im still looking for more power

YoungGunXR: check this out dyno ,xr650r, airbox mod,high flow airfilter,big-gun exhaust and ofcourse the edelbrock. its from my xr650r that i had, :cry:

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I appreciate all these posts as I'm in the same boat. I've done all the GM's and have ordered an Edelbrock from Barnum's based on some feedback here as well as some dyno charts. Doing it more for fun than anything else, but easier starting is always nice too.

Maybe a pipe will be next but I'm in no hurry and they're pricey too...

Not ready to mess with bore kits yet (less than 50 hrs on it).

(Also, how do you attack the suspension when you're in the middle of nowhere (and Canada to boot) and no specialists within 2000 miles???)

:cry:

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There are 3 octane rating systems. You should check to see what the "98 octane" is compared with what we use as a baseline. In the USA, most pump gasoline is 87, 89, or 91 octane. Sometimes 93. If your 98 octane is comparable to our 98 octane, there must be a reason why the higher octane rating is sold. Cold weather or just a lot of Ferraris out there?

You'll never get the power you had with the 650R, no replacement for displacement (or water cooled engines). The pumper carb will put a lot of snap into the engine when going from low to higher RPM.

The beauty on an XR is the simplicty and low needs. I'd stick with a lower compression piston to avoid having to use race gas.

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we got 95,96 and 98 gas (unlead) not so many ferraris, but maybe colder weather :cry:

it sounds that a pumper carb might be enough, those times when i miss the power is when i want to snap the throttle to raise the frontwheel or to set the backwheel in spin in the ~3gear .

which pumper carb is better?, the mikuni or edelbrock?

the only times i miss the xr650r is when i had the motard wheels on it, that was fun, althou the cops didnt like it :cry:

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Hey DWD, I didn't mean any offense earlier. I found a noticable loss in the "snap" of my bike when I took off the White Bros E Series pipe and reinstalled the stock pipe. I've still got the E Series, and I'll do a side-by-side comparo after I've modded the stocker and tweaked the carb, air filter and airbox a little. You may be able to try out a friend's pipe on your bike (it's only a five minute switch) to see if that gives you any help for a lot less cost and trouble than a new piston or carb. Larry

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Holy crap that xr650r had some torque! Nice :cry: What do you mean you cant get the front up in 3rd on the 400? Maybe its just the mods on my bike but I can do 4th gear wheelies sitting down. 5th gear standing. Still there isnt anything like doing wheelies on the 650. Almost too much power. :cry: My brother is also thinking about the 710-720 bore kit on it when he needs a rebuild. :cry:

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when i bought my xr400 i was realy dissapointed in the power that the stock bike had. after a few trips out, and a few spills cuz of the lack of snap at certain rmp's i started tinkering. what i found is the combination of a new performance pipe(mine was from xronly.com), a k&n filter, and messing with the jetting i was fully rewarded. this is about the cheapest way i can think of adding the nuts u r looking for.

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Last summer I got my stock 98xr400 after riding a 99 cr250 for a year and I to was looking for more power. So i went and bought and XRs only pipe and changed the sproket and rejected it and it was sweet. Then i got a little better at riding trails and took some advice from my boss who aslo has a xr400 and got a mikuni pumper carb which was the best mod i ever did to my bike. and after a summer i gotbored durnig winter amd with the advice of the local honda shop I bored it out to 416 and went with the 11 to 1 compression. As of right now im installing the 440 kit but still keeping with the 11 to 1 commpression. BTW I still have my cr250 and in a drag from stading start a nicley modified XR400 willl run neck and neck with a 250. also before u do anything on ur bike get a pumper carb it makes the bike come to life. I will advise to buy an extra kick start pedal with ur big bore kit so u can replace ur opld one after u break it learnign the new starting procedure with the higher compression. But boring it out is way worht the effort. but watch out if ur like me and ur a young kid with to much money and to much time on his hands u'll be drop some major bucks on ur bike

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