Removing adapter bush from carb / TM40 disassembly?

Discussion in 'The Garage' started by clintnz, Sep 10, 2019.

  1. clintnz

    clintnz Trans-Global Chook Chaser

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    So I got a good deal on a barely used Mikuni TM40 flatslide to replace the elderly BST40 CV carb in my KTM 640:

    [​IMG]

    It's off an XR650R & the intake & outlet were both too big. I was able to chuck it up in the lil' lathe & machine down the smaller engine end to fit, but the airbox end has stuff in the way. so I need to get the adapter bush off so I can machine a few mm off it. I'm guessing it is glued on & enough heat would get it off, but I'm worried about fubar-ing rubber/plastic bits in the carb. Any ideas welcome.

    (yes, welding a nut to it is on the list. Just not high on the list :lol3)

    The other option is to dismantle the carb & remove the intake spigot. However the fact that this part is held on by security screws suggests to me there may be a bunch of parts inside that will go SPROING! all over the workshop & be difficult to put back properly. So if anyone has any info or links to resources on tearing down a TM40 I'm all ears.

    Any jetting or setup hints would also be appreciated, I think she should be pretty close but I'm a n00b to flatslides.

    Cheers
    Clint
    #1
  2. shovelstrokeed

    shovelstrokeed Long timer

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    Wouldn’t it be easier to modify the air box?
    #2
  3. jimroid

    jimroid Been here awhile

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    Is it a straight inside bore or tapered? If straight , machine an aluminum mandrel, drill and tap with 1/2”npt , make two cuts 90 degrees apart, insert pipe plug to tighten inside carb . Machine carb while chucked on mandrel. Make sense?
    #3
  4. jimroid

    jimroid Been here awhile

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    Quick example, OD would be turned to carb ID to expand and lock carb on while turning your oversized bell off. 9BF39B70-85A9-4A5F-934C-241ED9277167.jpeg B5B88275-70E4-4598-AD55-84CF9A4E1D82.jpeg 2EB7A2E5-5A5B-4C8F-842E-27E5E5876B70.jpeg
    #4
  5. clintnz

    clintnz Trans-Global Chook Chaser

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    There may be room to make some sort of adapter boot in between carb & airbox but it would be way tidier to machine down the TM40 carb to match. I'd like to keep as much of the bike std as possible so swapping back to the original carb is easy, with it being Mikuni/Mikuni the throttle & enrichener cables go straight on.

    Makes perfect sense but the problem is that the lower carb body is in the way of getting a cutting tool in to the back of the adapter sleeve & I'll need the full depth of it. I think if I get the sleeve off I'll need to machine it on a mandrel anyway as it will end up fairly thin.

    Cheers
    Clint
    #5
  6. jimroid

    jimroid Been here awhile

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    From your angled picture I don’t see the hurdle. Maybe a side profile picture? It’s probably shrunk on, maybe just slit it and it will fall off?
    #6
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  7. clintnz

    clintnz Trans-Global Chook Chaser

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    I need to take off 6mm on Dia, & ideally shorten it up by the same. This takes me back down the chamfer a ways.

    [​IMG]

    Chopping it off would be an option. I'm also toying with the idea of making a tool like an inner bearing race remover to heat up, clamp on & hopefully twist it off.

    Cheers
    Clint
    #7
  8. ohgood

    ohgood Just givver tha berries !!!

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    1 remove the four bolts and clamp it to a plate, turn down the od, reinstall ?

    or

    2 hack saw slits along either side and toss the bell adapter in the can, then turn your own ?
    #8
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  9. Beezer

    Beezer Long timer Supporter

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    another idea... it looks like that piece is either glued, screwed, or heat shrunk. put a slit in the piece all the way through with a moto tool cut off wheel & see what happens. if its a heat/shrink you can just pull the piece off once it's broached. likewise if its a screw (usually screw/shrink). if its glued I would make a series of cuts and heat each segment until it pries off. put the carb body in a bowl of water while you work with heat if its getting too hot
    #9
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  10. clintnz

    clintnz Trans-Global Chook Chaser

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    Thanks guys, some good ideas there.

    Looking at drawings of the carb, the slide guide is part of the inlet spigot (part #10), so it would be a little fiddly to fixture, but I think removing it & machining down the bush without removing that will be the way to go as it will save me having to make a mandrel etc.

    [​IMG]

    Cheers
    Clint
    #10
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  11. katbeanz

    katbeanz earthbound misfit, I Supporter

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    On the TM40 I have the adapter is shrink fit with loctite as backup, probably 0.002" interference fit. Now you can use the level of heat required to expand the adapter and soften the threadlock if used on yours. If things go bad, see if shipping rates from 64118 are feasible, or send a pm. :deal
    #11
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  12. Beezer

    Beezer Long timer Supporter

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    if part #10 comes off, it looks like it would be no problem in a 4 jaw chuck if you really want to lathe it
    #12
  13. jimroid

    jimroid Been here awhile

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    Got that 640 tuned yet?
    #13
  14. clintnz

    clintnz Trans-Global Chook Chaser

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    Cheers guys. Part #10 came off with only one tiny part flung off across the workshop (fortunately found) I had a go at making a mandrel to hold it for machining but there is a slight taper in the bore so that was a no go. On to plan B next; router out a profile in a piece of 1" MDF so I can screw #10 to it then hold it in the 4-jaw. Weekend weather was too nice to spend all of it holed up in the shed.

    Fitting it to the bike & tuning will be some way off as after Thursday opportunities for quality shed time will be minimal for a few weeks. Hopefully the XR650R tune is pretty close.

    Cheers
    Clint
    #14
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  15. clintnz

    clintnz Trans-Global Chook Chaser

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    Special tool #666-650-640 ready for action:

    [​IMG]

    2016 router to 1947 lathe...

    [​IMG]

    Done. Didn't have any parts left over so it must be good right?

    [​IMG]

    Main jet is 140 vs the 160 in the current carb. Is it normal for a flatslide to use a smaller main than a cv carb?

    Cheers
    Clint
    #15
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  16. shovelstrokeed

    shovelstrokeed Long timer

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    There is no telling just by the number as jets and coding for size can vary from model to model and mfg to mfg.

    You now have the fun task of sorting jetting and fun things like slide cutaway, needle position and dealing with reversion.
    #16
  17. Beezer

    Beezer Long timer Supporter

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    what he said.... Mikuni, Kehin, and Dynojet with the same number are all a different size. different length & approach angles too. if you don't know exactly whats in there consider getting a matching set of know components. mixing brands leads to frustration

    [​IMG]
    #17
  18. clintnz

    clintnz Trans-Global Chook Chaser

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    Current carb with the 160 main is also a Mikuni, same 40mm bore but CV: BST40. Haven't pulled the jet outta the TM40 but it looked the same type.

    Some tuning fun in store no doubt, a lot more to fiddle with on this vs the old BST, but hopefully the XR650R tune is pretty close.

    Cheers
    Clint
    #18