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Old 03-11-2011, 10:58 PM   #16
Brtp4 OP
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Bike Choice Part 4

My other bike is an 06 XR650L. I've done lots of mods to it, CRF forks, FCR carb, 672 kit, cam, big brakes, etc., and stripped off a lot of weight. It works really well, much better than stock, but is still heavy. The idea of something that was the exact opposite in some ways (shorter, lower, quicker steering, lighter) yet having some of the good characteristics (low revving, linear power, super reliable) was really appealing.

On the other hand.....it's a playbike, not a race bike. Kinda slow, budget suspension, low tech motor. But I kept coming back to a few things: the short wheelbase, 6 speeds with fairly close spacing, a Honda, and the mild state of tune. The wheelbase and gearing would make it competent with more modern bikes in tighter stuff, perhaps even be an advantage. The XR factor meant it would be super reliable and easy to mod, and the mild state of tune meant that I should be able to get more power from it easily. Just a simple compression bump and pumper carb would be big upgrades. A CRF250 has considerably more power, but the XR has a good delivery and probably a lot of potential. Here is a graph of the two:



If you run them in the upper half of the range, the XR will get smoked bad. If you run them in the lower half, the XR is as fast or faster. If there is on thing about the CRF that really stands out, it is not the peak HP, rather it is the fact that the power curve is really flat for a wide spread at or near the peak HP. The XR really drops off.

More.....

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Old 03-12-2011, 01:30 AM   #17
n16ht5
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wow, looks like a great build! Going to be one nice bike.

I have an 01 XR250R, wouldn't trade it for anything. Definitely subscribing to your thread. I never knew about those triples, going to look into that. How do you like the FMF ..Q4?

My bike doesn't have much for engine mods... mostly everything else. when it needs a teardown I'll open it up to 300CC

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Old 03-12-2011, 06:55 AM   #18
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Originally Posted by n16ht5 View Post

That bike is nice, where you live is even better!!

The Q4 is really nice. I have a PC pipe on my other bike, build quality is sliiiiiightly better but the FMF is quieter.

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Old 03-12-2011, 07:33 AM   #19
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Most of the time I am riding on unfamiliar trails, which requires a totally different style of riding for me. On familiar rides I can memorize braking and turning points, and can have the revs where I need. On unfamiliar stuff, I have to read it, process it, and then ride accordingly. Not being 25 any longer means reactions and endurance fall off. I can still ride aggressively here and there, but when I do I often fall behind the terrain and make mistakes. You just can't do this consistently without hitting the ground from time to time.

When I was younger I was far more aggressive. I was not, and am still not, that fast, but I would try to make up for a lack of talent by trying harder. A while back I figured out that I needed to modify my riding style in order to avoid hitting the ground and still ride with guys faster than me. I do some mountain biking also, and not having a motor taught (forced) me to be efficient. One of the guys I ride with is about 160 lbs (I am 215..) and super fit. Having a motorcycle background, I can descend faster than him, but he can out-pedal me anywhere. But there is this one trail near me that ends many of the local rides. It's about 2 miles long and flat, with lots of quick left/rights. Despite his better fitness, legs, lighter bike, etc I always smoke him here. He can accelerate faster than me, but is a total puss in the turns. He'll fly up to them too fast, grab the brakes, roll through, and pedal hard out. I roll up slower, little or no brakes, get a couple pedal strokes IN the turn, and keep spinning out. I am always on the pedals, he is on, off, on, off. After a few turns, I am usually gone. The funny thing is, when we get back, he'll always say "man, you are so much more aggressive than I am there", when in reality, I am less aggressive....just more smooth.

This has become my target for this project. The plan is to make the bike easy to ride for long periods, quick turning, and to increase the snap of the power. The power output is fine, it just needs more snap to help with obstacles and direction changes. People often focus too much on having HP when the real goal is to have the throttle on as much as possible, driving you forward. Anyway, I know I am going to give up a lot in terms of peak power, but adding a pumper carb and some compression, combined with the 6 speeds and mild power delivery, should facilitate a good average speed. And on faster wide open desert stuff, well, I don't really want to be hauling ass there anyway. Plus I have the 650.

More....

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Old 03-12-2011, 01:26 PM   #20
HighwayChile
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interesting on the dyno specs, you should be close after some mods, with far better reliability - esp in the valve train area.
what you are describing above in riding style is what under powered 4 stroke riders subscribe to, works well
Great thread
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Old 03-13-2011, 07:18 PM   #21
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Tires, Tubes, Gearing

Generally I am a Michelin guy, so I picked out some M12 XC tires based on a recommendation from a friend. I got a 130/80x18 rear, and it is a little smaller than other tires with the same numerical size. Seems perfect for this, not too much tire. We'll see.

On thing I did do was to put both tires in with Bib Mousses. I can tackle most work on a motorcycle excluding bottom ends, but I friggin hate changing tires. Since I will not be doing extended slab on this, I decided to sidestep the whole thing and use the Mousses.

On gearing, I am looking at it like a work in progress. I usually gear down, but in the case of the little XR, some people say that you should gear them up. I looked at trans and final drive ratios, and sprocket gearing, and this seems to be true.

I initially figured I would both gear up, and try to slow chain speed also. Stock gearing is 13/48, or 3.69. I looked at various application charts, and decided to go with 14/49, or 3.5, a mild difference. Ordered up a popular branded front sprocket and a Renthal Alu carrier / steel ring rear. These are great for saving weight, yet still fairly strong:



These XRs will accept a 14T front, but fit is so tight, you have to modify the stock case guard. The stocker is so flimsy, it seems useless as it is, and grinding it can't help. Throwing chains through the cases is far, far too common, and where I live it can strand you and cause a serious pain in the ass. Additionally. I had decided to use an XRs only guard, but they do not make one for a 14T.

I do not want to have any chain, meet transmission issues, and had to have a good case protector more than 14/49 gearing. Reliability is key, and in the hands of the guy choosing and installing the parts. So basically, I set my 14/49 gearing on the shelf, and ordered a 13/45 (3.46) set from Supersprox:



Everything gets blue Loctitite, especially sprocket bolts:



Sprocket w/XRs Only Guard:



Looking at this, I decided two more things: first, ANYTHING I can do to strengthen the guard and minimize the possibility of case damage, the better; and I don't want to suck the cuff of my over-the-boot pants into the chain. The stock guard would not fit, but I did some Dremeling on it:



cleaned it up with a wire wheel:



And got it to fit. I now have a stronger case protector, and it looks like stock:



Continuing on the theme of heading off issues before they happen, I added an IMS shifter. It does not function any better than the stocker, but the shape places it differently, and the thicker material makes it less likely to punch through the cases in a fall. You can see the PO already gouged the cases with the stock shift level, BTW. I will eventually make a reinforcement and attach it to the side cases somehow.

More....

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Old 03-13-2011, 08:19 PM   #22
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Old 03-13-2011, 08:50 PM   #23
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you

Brian if you do a search for ENGINE CASE SAVER GUARD PLATE HONDA on eSlay you will find what you need for your shifter protection on the case.

Looks like it will be a fun little bike. I would be a little scared on something like that LOL. My fat ass would get to comfy in the idea that I could throw it around

Looking forward to following the build
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Old 03-15-2011, 10:19 PM   #24
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Breathing

Getting these to breath is fairly simple. In my case, The first step is to correct the OE Honda exhaust flange welds. For some reason, Honda welds up the pipe to the flanges unbelievably sloppy, so that the pipe is restricted 20% or more of its diameter. They do not bother to grind it, just bolt 'er on. Take a look:



That is not carbon buildup, it is the weld!

A good chunk of time with the Dremel and you can begin to see the difference on the left side of the flange. This is still not finished, but it was so tedious I forgot to take another photo:



For the silencer, the stock one is not that heavy and worth keeping. There are inserts available on EBay that make it flow well, for very little $$$. But I wanted the looks factor of an FMF Q4:



Workmanship is great and the bike sounds good and is not loud.

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Old 03-16-2011, 10:02 PM   #25
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Nice build up. I love xr250's most under rated single track bike ever.
I don't know how that m12 will behave on the little thumper, but on bigger bike's it has a tendency to step out sideways under throttle instead of driving forward. To me the s12 is the ultimate rear tire.so predictable, so consistent.
paired with either a s12 or m12 front, depending on terrain.
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Old 03-17-2011, 12:00 AM   #26
bobfab
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Awesome build! Nothing quite like the air-cooled honda trailbikes!
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Old 03-17-2011, 07:46 AM   #27
hanksmybuddy
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What kind of gas mileage are expecting out of the 250 with the pumper carb?
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Old 03-17-2011, 08:03 AM   #28
Moto Beak
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Awsome project! I had an XR250 in '96, and I loved it. Half of the fun is the simplicity. I raced it a bit (this was before the current crop of higher performance four strokes) and beat a lot of bigger, "faster" bikes, gettign top three finishes in the four stroke B class. People don't like getting passed by a little trail bike.

Definitely get the suspension properly set up. I found out the stupid way that these bikes can go a lot faster than the suspension will tolerate. And watch your toes! Ten inches of travel leaves them in harm's way quite often.
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Old 03-17-2011, 08:15 AM   #29
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Awsome project! I had an XR250 in '96, and I loved it. Half of the fun is the simplicity. I raced it a bit (this was before the current crop of higher performance four strokes) and beat a lot of bigger, "faster" bikes, gettign top three finishes in the four stroke B class. People don't like getting passed by a little trail bike.

Definitely get the suspension properly set up. I found out the stupid way that these bikes can go a lot faster than the suspension will tolerate. And watch your toes! Ten inches of travel leaves them in harm's way quite often.
Thanks for the tip on the suspension, and that is a very, very smart tip on the toes. I have already been bitten by it on the 1st shakedown ride, smacked a lava rock BUT GOOD. I am going to have to remember to keep them pointed up, otherwise I'll be folding them around the footpeg.

What did you do to your suspension? What's your weight and what spring rates did you get?

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Old 03-17-2011, 09:44 AM   #30
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I had an '01 with 285 kit, hot cams, full exhaust system, ( i forget what brand) and ohlins forks, The bore kit was the single best mod, if i had it to do over again I would probably not do the hot cams, i don't think they really did that much for me, although to be fair I did not upgrade carb or stiff valve springs. There are weld on adapters that widen the footpegs that helped me keep my toes up.
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