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Old 03-12-2011, 02:26 PM   #16
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, 08:18 PM   #17
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Tires, Tubes, Gearing

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.

On thing I did was to put both tires in with Bib Mousse, as I hate changing tires. I will not be doing extended slab on this, so they should hold up well.

On gearing, in the case of the little XR, some people say that you should gear them up. Stock gearing is 13/48, or 3.69. I looked at some application charts, and decided to go with a 13/45 (3.46) set from Supersprox:



Everything gets blue Loctitite, especially sprocket bolts:



Sprocket w/XRs Only Guard:



Once I added the XRs only guard, the stock cover would no longer 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:

More....

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Old 03-13-2011, 09:19 PM   #18
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Old 03-13-2011, 09:50 PM   #19
TourPros
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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, 11:19 PM   #20
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Exhaust

The first step toward getting these to breath is to grind the awful OE Honda exhaust flange welds. Honda welds up the pipe to the flanges unbelievably sloppy, so that the pipe is restricted 20% or more of its diameter. Take a look:



That is not carbon buildup, it is the weld itself. Some time with the Dremel and you can see the difference on the left side of the flange.



Added an FMF Q4:



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

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Old 03-16-2011, 11:02 PM   #21
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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, 01:00 AM   #22
bobfab
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Awesome build! Nothing quite like the air-cooled honda trailbikes!
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Old 03-17-2011, 08:46 AM   #23
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, 09:03 AM   #24
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, 09:15 AM   #25
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Quote:
Originally Posted by Moto Beak View Post
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. What did you do to your suspension?

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Old 03-17-2011, 10:44 AM   #26
sporthog93
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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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Old 03-20-2011, 08:30 PM   #27
Moto Beak
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I didn't do anything to the suspension. The last time I raced the bike I broke my hip, going too fast for the suspension. I was stupid for not knowing better. After healing up I switched back to two strokes. I would expect you could get good results with the stock components (with revalving and springs), but upgrading the suspension would be a good idea. That is a whole different project in itself.
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Old 04-22-2011, 10:31 PM   #28
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Breathing Part 2

One of the disadvantages of older 4 strokes is poor throttle response. Newer bikes have light flywheels, and carbs with accelerator pumps, and the extra snap helps immensely.

I was thinking about a Keihin FCR 35 and Sudco listed a kit for the XR. So I ordered it up.







Side by side with the stocker:



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Old 04-22-2011, 10:45 PM   #29
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Test Fitting

First thing to do was to test fit the carb to see how it fit, how cables routed, etc. It was a bit of a hassle to get into place, but once in, fit fine:







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Old 04-22-2011, 11:02 PM   #30
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Parts needed:

A few additional parts were needed to fit it. First, the throttle cables come off the stock carb on the left side, on the FCR they are on the right. Additionally, they are really close to the upper motor mount:



I called Motion Pro, and they sent me cables with 45 degree elbows. I had to be really careful so they did not contact the cylinder head and melt the housing. Additionally, the bracket is threaded, so I had to spin the cables into the bracket before putting the carb on, otherwise.....not enough room to spin the cables into the threaded bracket. I ended up carefully drilling out the threads on this bracket:



Once I got this done, it was much easier to fit, position, and adjust the cables.
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