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Old 03-20-2011, 07:30 PM   #31
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, 09:31 PM   #32
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Breathing Part 2

One of the disadvantages of older 4 strokes is throttle response. Newer bikes have carbs with accelerator pumps, and once jetted correctly, the extra snap helps immensely with obstacles, breaking the rear wheel loose, etc. My plan for was to have the bike be nimble and snappy, and I figured I needed to ditch the stock carb to accomplish this.

I was thinking about a Keihin FCR 35 and Sudco listed a kit for the XR. A few people said it would not fit. But Sudco siad it did, so I dug a little deeper, and finally found pics on an Italian site of a 250 with an FCR35 on it. So I ordered it up.







Side by side with the stocker:



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Brtp4 screwed with this post 07-27-2014 at 06:11 PM
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Old 04-22-2011, 09:45 PM   #33
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Test Fitting

First thing to do was to test fit the carb, so I could get some scope of the project. I did not have the correct intake boot yet, but wanted 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, 10:02 PM   #34
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Parts needed:

A few parts are 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 Ed Willis at Motion Pro, and he set me up with cables that have 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 ( know, confusing). 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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Brtp4 screwed with this post 07-27-2014 at 06:12 PM
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Old 04-22-2011, 10:11 PM   #35
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The airbox side OD is bigger, so an XR400 boot is needed:





One thing that is different, and still unresolved, is the crankcase venting. My bike is a California model, and had a more extensive crankcase recirc system. The 250 boot has a boss to attach the hoses to, that the 400 boot does not have.



Also, I noticed that the stock intake manifold had hardened considerably, so I took no chances and replaced it.

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Old 04-22-2011, 10:39 PM   #36
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AP Timing

The biggest part (hassle) of the carb install was figuring out how to time the accelerator pump.

Several people let me know that I had to 1. time the squirt to start a little late, and 2. limit the duration of he squirt to 1.5 secs, to not bog the motor.

The newer FCR-MX pumpers have a leak jet, which can be changed out to control the squirt. A larger jet bleeds feul out of the circuit instead of pumping it into the motor. It is quantitative and works well. But, the older FCR slant body carbs like the 35 do not have leak jets. There is an accessory from Boyesen that duplicates the bleed-off, so I got one to try:





and mounted it up:



I started testing the squirt off the bike, with odd results. The pump would hesitate, then squirt for what seemed like forever, definitely not 1.5 seconds. No amount of adjusting was helping, and I was getting confused.

By now I had burned a load of time and money ordering various diaphragms and add ons, and was getting kinda frustrated. I finally decided to just send the carb to Eddie Sisneros ("Burned" on Thumpertalk) and have him set it up. After a few days , Eddie calls me and says - get this - THE SQUIRT PASSAGEWAY WAS NOT FULLY OR PROPERLY DRILLED FROM KEIHIN. W.T.F!!!! He describes it and says "yeah, the thing would hesitate and spit, and then squirt forever. I drilled the hole, wired the AC pump linkage, and now it is fine." My lack of experience, I would have never spotted this, and would have chased the squirt timing forever.

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Brtp4 screwed with this post 07-27-2014 at 06:14 PM
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Old 04-23-2011, 07:55 AM   #37
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Verbage, more verbage, some more friggin verbage, pics, more pics, blah blah blah. When in the hell do I get to flog the shit out of that thing, break something, so you can work on it some more.
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Old 05-26-2011, 05:33 PM   #38
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Any updates. I am in a similiar position myself. I have a dr650 that I modded with rmz forks, cogent shock, fcr carb, gsxr exhaust and a long list of farkles. It does great for dual sport rides where we may cover half the state in one day on dirt roads, railroad beds and trails. The tougher atv trails in this area tend to be mud, rocks and roots, not as much fun on a big bike. I keep thinking about adding a smaller bike for the tight stuff.
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Old 05-26-2011, 11:04 PM   #39
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Yes, some updates. Did two rides. Power was very good, some jetting circuits are way off. I started with the following jetting specs:

Slow air screw 1.25 turns
Pilot 42
Fuel Screw 2.5
Needle CEMT #2 position from top
Main 140
Boyesen 1.5 turns out


I did some short runs around the neighborhood, and these settings were close. So, I went for a shakedown ride at Cline Buttes, nearby here. It is mostly flat desert singletrack, kinda loose, and whooped out in places.


First, the bike starts like it has been sitting three years. Kick about a 10 times,, sputter, kick x10, sputter longer, kick 10x, sputter longer again, eventually it ran. Once it got warm, it would run well when it got up onto the main jet. But the pilot circuit, needle, AP pump, are all still off a bit.


Power was better than I thought. It is not fast, but it makes consistent, steady power. It is a little sloppy - I had to slip the clutch out of turns to get past a flat spot. Once I get it dialed it will be better.


Few things I did not like. I did not touch the forks yet, but they were not bad. The back though....sucked. It bounced and deflected off every rock, and I generally tacked back and forth down the trails all day. I don't know if it is acclimation, or tuning, or whatever, but I need to correct it.


Another thing that is a real problem: the footpegs are too low. I was paying attention, and skimmed rocks several times. I have been told this by others, but it is a real problem. If you are not careful, it is dangerous.


Basically, I think I am 90% of where I wanted to be with it but in different ways. I thought the power would be disappointing and the handling would be dialed. Instead, it is the other way around....power is adequate and easy to use, and I adapted to it right away. But the chassis requires bigger changes in riding style than I thought, and needs to be dialed in. It was actually decent in whoops but skipped around a bunch in the rocks. Plus the jetting is way off.

Hope that helps.

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Brtp4 screwed with this post 07-27-2014 at 06:17 PM
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Old 05-27-2011, 06:48 AM   #40
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Old 05-27-2011, 07:33 AM   #41
hanksmybuddy
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Way too much technical jargon bullshit here. Just ride it somewhere cool and give us friggin pictures. We don't need all the other bullshit!

Call me when you want me to school that thing with the KDX!
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Old 05-27-2011, 08:19 PM   #42
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Quote:
Originally Posted by hanksmybuddy View Post
Way too much technical jargon bullshit here. Just ride it somewhere cool and give us friggin pictures. We don't need all the other bullshit!

Call me when you want me to school that thing with the KDX!
Did you know they make a CRF 250X? You could probably pick one up for about the same price as half your mods JK I spent way too much on my 125 so I know what it's like
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Old 05-27-2011, 08:45 PM   #43
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Fair enough...
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Old 05-27-2011, 09:14 PM   #44
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Quote:
Originally Posted by hanksmybuddy View Post
Way too much technical jargon bullshit here. Just ride it somewhere cool and give us friggin pictures. We don't need all the other bullshit!

Call me when you want me to school that thing with the KDX!
I'll dissent. Vey useful information here as far as XR setup is concerned. Keep up the good work! I've got an older XR250L that I just unexpectedly picked up due to a very low price, and this thread, while not directly relevant due to generational differences between our XRs, has been a great source of information. Thanks again - looking forward to reading more about this bike in the future.
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Old 05-28-2011, 07:44 AM   #45
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Don't worry about Hanksmybuddy....he's a riding buddy. All good.

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