640 FCR 37 install

Discussion in 'Thumpers' started by gunnerbuck, Oct 16, 2012.

  1. gunnerbuck

    gunnerbuck Island Hopper

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    After reading a few positive posts on running an FCR 37 in place of the BST I decided it was worth a try so I picked out one out of the many listed on EBAY... The one I ended up with came from a 05/06 RMZ 250 and had all the cables and the twist grip... The box showed up in the mail and upon first inspection the carb looked to be in good shape... This particular carb had the usual enricher circuit but was equipped with a hot start circuit as well...The slide looked good with not to much wear showing so I cycled the throttle cam, as the slide lifted out came a shot of rotten smelling fuel from the A.P. nozzle... I was thinking, wow this guy mailed out the carb and did not even empty out the crappy fuel, at least I know the A.P. is working... I then pulled the float bowl and noticed that there was quite a bit of rotten fuel varnish coating the inner workings so I ordered up a rebuild kit... The throttle cable also looked a bit pooched so one for an SXC is on the way...

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    The first thing I noticed when comparing is the bell to bell measurement on the FCR is about 15-20mm shorter than on the BST..
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    Also the FCR has a smaller air box end Bell
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    I did some measuring and found that I could make an adapter piece out of some 2 1/4" SS exhaust pipe...
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    Very close to the size required with a bit of work...
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    I ground the lip off the airbox bell end of the FCR and tested my sample adapter piece...
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    With some persuasion I figured it would fit so I coated the bell with 648 retaining compound...
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    I then heated the piece to expand it and persuaded it on with the help of a block of wood and a hammer... This proved to be a very tight fit, so much so that it will have to be cut off with a dremmel if I ever have to remove it...
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    I then measured the final product FCR against the BST
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    And see that to be perfect, I could of left a couple more MMs length on my adapter... Oh well, the slightly shorter length will make it a bit easier to install the carb when the time comes...


    Next up will be to clean out the carb and install the rebuild components when they arrive....

    I will also have to figure out what jetting to go with to fit my setup... I would imagine I could go with something similar to what guys are using on the FCR 39s for starters... I really don't care so much about increases in top end performance as I do about the bottom end trail power... I am hoping to get a little more front end lofting snap out of this carb to help when bouncing small logs, rocks, roots and other trail obstacles... I would like to tune this in leaving the snorkel and airbox intact therefore keeping with the water tight integrity of the original design...


    f
    #1
  2. ChrisC

    ChrisC Amal sex?

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    #2
  3. bmwktmbill

    bmwktmbill Traveler

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    Ditto.

    I wait in amazement.
    bill
    #3
  4. gunnerbuck

    gunnerbuck Island Hopper

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    I'll get back on this in a few days when my parts show up....

    Does anyone have some jetting #s that they are using in a 39 for comparison? I haven't looked at the #s of whats in the carb right now but looking at the Suzuki parts data it lists a 178main, 42 idle pilot, 100 idle air, #68 starter,#60 power as stock for this carb....
    #4
  5. juames

    juames Have Fun, Don't Die!

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  6. smokeeater495

    smokeeater495 Been here awhile

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    I hope your homebuilt spacer works for you. I read a test where a guy put an FCR39 on his XR650L with an exhaust pipe adapter and it ran like crap. Google "Noss adapter". It attaches to the intake side of the carb and provides a smooth transition. The 37mm carb should have awesome low end snap.
    #6
  7. gunnerbuck

    gunnerbuck Island Hopper

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    After a bit of a wait the parts showed up yesterday...

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    I paid about $33 shipped for the longer cables and around $28 for the carb kit..
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    I was pleased to see new jets in the kit with the main being a #162 VS a #178 that came with the carb....
    The big thing is to try to figure out a starting point for the jetting, the #162 may be ok as I think the SXC runs the next size up on a FCR 41...
    The jetting info I pick up on line is not very use full as most people that swap carbs also gut the airbox and add a more open exhaust.. So I'm kinda going by trial and error with this thing...
    #7
  8. gunnerbuck

    gunnerbuck Island Hopper

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    Part of the XR 650 guys problem could of being getting the pipe to properly seal... I pressed mine on with retaining compound and once I get the thing fully cleaned up I will add a bead of sealant around the pressed on rim just to make sure air can't leak in...

    I was going to get my machinist friend to make me up an adapter but he was busy at the time so I figured I would try the SS pipe for a start... Even without the adapter the FCR has quite an abrupt entrance into the bell... The SS pipe really doesn't change anything with that except adding a longer throat to the airbox... If it turns out to run poorly I'll think about adding a stabilizing vane to the throat...
    #8
  9. johnno950

    johnno950 Long timer

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    I had a lc4 with a 39mm fcr (carb from a jap bike),the bell could be ordered from ktm to fit the carby,if the 37mm is the same as 39mm, have a look at the part numbers from a 00-06 ktm 660 rallye.
    #9
  10. gunnerbuck

    gunnerbuck Island Hopper

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    Some of the FCR 37s have a bolt on bell that can be changed and some don't... This carb is not the bolt on bell type...
    #10
  11. Droptarotter

    Droptarotter Long timer

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    You were working on that late last night Gunner!

    Cheers
    #11
  12. gunnerbuck

    gunnerbuck Island Hopper

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    Must of been half asleep too looking at my last post..
    #12
  13. gunnerbuck

    gunnerbuck Island Hopper

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    I'm still waiting for an extended mixture screw which I hope shows up tomorrow, in the meantime I started the tear down and clean up of the carb...

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    There was quite a bit of varnish inside and the power jet was completely clogged and needed the help of a piece of wire to clear it..
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    Still a bit of varnish showing but most of it came off with carb cleaner and a tooth brush scrub...
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    My part comparison chart, new VS old...
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    Now to figure out which combo to use upon assembly to be in the ballpark... I think the 162 main may be a better choice over the 178, I'll use the 42 pilot... The SXC runs a 85 starter jet so we'll see if the 68 will be big enough... The power {leak} jet is a bypass jet so the smaller the # the more fuel goes into the A.P. , I will go with the #55 for starters...
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    I dont know what this needle is for but it is way off for this application...
    f
    #13
  14. gunnerbuck

    gunnerbuck Island Hopper

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    [​IMG]
    The other day I put a thick bead of sealant around my adapter to make sure no air could leak in and now it was dry... I rigged some vent hoses...
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    I found and soldered on a male TPS plug that fits the FCRs port so that made it simple..
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    I rigged a bridge vent to eliminate 2 of the 4 hoses and then ran one tube to the airbox and the other down behind the swingarm..
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    It was a tight fit and I had to jockey around some hoses... I got everything hooked up and then rolled the bike out to give it a test with a remote tank...
    After about half a dozen cranks to advance the fuel she fired up in a startling fashion...
    The good news is that it runs great at over 5000 RPM but the bad news is: I was unable to test the bottom end power because the revs wouldn't drop below that... I called it quits after that... Next I'll have to see where the fuel is leaking in from to give it the high revs, likely the slide is sticking and not bottoming...
    f
    #14
  15. B-Rod

    B-Rod RubberNecker

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    An FCR on a 640 would be fun fun fun. Maybe fire off a message or call Motolab. He might have some jetting suggestions, or even JDjetting. To me a 162 main at sea level sounds lean for the air a 625cc pumps through :dunno
    #15
  16. gunnerbuck

    gunnerbuck Island Hopper

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    162 is the closest of the 2 jets I have on hand, remember the SXC with a 41 FCR only runs a 165 in stock form... My airbox has been left stock so the current jetting shouldn't be too far off...
    #16
  17. B-Rod

    B-Rod RubberNecker

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    If you do need jets in your fine tuning, you'll probably find that any shop that sells dirt bikes will have a box o' jets somewhere handy. I've found everything I needed locally. I don't really know the difference between the long and short mains for the FCR, but I've successfully used either in two different bikes. Seems to work just find with either. Maybe I'll look it up one day.
    #17
  18. gunnerbuck

    gunnerbuck Island Hopper

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    Well, I found why the bike was stuck at half throttle... The fault goes with the motion pro cables... It turns out the cable is too short, more specific there is not enough cable end free of the sheath... So when it is put in place the throttle cam has a little tension on it and lifts the slide.. The sheath is set as short as possible and the cable end is still 3/8" too short so I will try to trim a bit off of the sheath to buy some more length on the cable exposure...

    I have heard some complaints about motion pro cables, this is my first trial on one and so far I say they suck....
    #18
  19. gunnerbuck

    gunnerbuck Island Hopper

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    I shortened up the cable and gave it another test run... Was lean down low with a bit of a hang before the revs dropped to idle...So I swapped out the 42 pilot for a 48 and raised the needle one position... I tried it again and it idled nicely and throttled up cleanly...

    The issue now is the bike will stall when I rapidly snap the throttle open.... I think a bit of play time with the A.P. is in order to fix the stalling, it may not be getting a big enough squirt... I ended up throwing the BST back on for now and will go back to playing with the FCR at a later date....

    Running the BST again showed me how much more snap in my brief bit of testing the FCR 37 gave my engine...
    #19
  20. Droptarotter

    Droptarotter Long timer

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    Gunner;
    FCR's usually come with a 3 second squirt on the AC pump. That's usually way too much fuel.
    I tuned mine on my 520 EXC to 1 second........that made a huge difference.

    Cheers
    #20