Swapping carburetors question

Discussion in 'Tech Area' started by Turbottt10, Oct 13, 2018.

  1. Turbottt10

    Turbottt10 New Member

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    Is it possible to swap a 1977 and earlier carb to a 1978 trail70??? I'm done screwing with this carb. Thank you.
     
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  3. racerx

    racerx Administrator
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    Not only is this possible, it'd be my first choice for replacing any of the later, less adjustable, carburetors. Only thing I cannot tell you, with certainty, is if there are any fitment issues. If there are, they'll be minor...and easy enough to fix, by swapping in an early-style intake or/and airbox. From what I've seen, that should be a non-issue. OER airboxes & parts have been physically identical with one exception - the carb-to-airbox boot. The newer type has been ~6mm too long...not ideal, but livable. The fix, when absolutely necessary, has been to trim the carb end of the boot. It ain't pretty, but it's not the end of the world either.;)
     
  4. Turbottt10

    Turbottt10 New Member

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    So if I'm understanding. I need to change to a early intake and possible a air box. Would I need to change the throttle cable also??
     
  5. racerx

    racerx Administrator
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    Apologies for any misunderstanding, my wording isn't always the clearest.

    Okay, first off I'd not expect any fitment issues. IOW, I'd get the carb and see how it fits. There's a very good chance that it will be close to "plug & play", with the difference being at the carb-to-airbox boot...and close enough that it'll work with a little extra oomph during assembly. That's where I suggest starting, rather than just throwing parts at it, from the get-go. FWIW, the later OER airboxes I've seen, firsthand, fit quite well on the early bikes, there are also new airbox boots available. If there's a clearance issue, where a shorter boot is needed, I'd try sourcing a new boot; at most, I'd order a new airbox canister only and just reuse the rest of the parts from your existing airbox. New airbox assemblies can be sourced but, they have to be assembled from bagged parts. So, unless you're after all-new parts, why replace more than necessary?

    As for the throttle cable,inner cable here again it's just a matter of minor differences. In a nutshell, your existing cable will have either too much, too little, or just the right amount of "stick-out length". If there's too little, you could clip a coil, or two, of outer sheathing. If there's too much, i.e. more than the adjusting barrel can compensate for, then the simplest fix would be clipping the inner cable to length, then installing a new end ferrule. That's a little involved, if you don't what you're doing. I'd source a new brass ferrule, for the handlebar end of the cable. Dratv sells these. It's more work than replacing the carb end ferrule...however...if your soldering doesn't hold, there's zero risk of a ferrule being inhaled by the engine. Again, it's worth test-fitting what you have. Odds are 2:1 in your favor.
     
  6. Turbottt10

    Turbottt10 New Member

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    Great explanation thank you for all your help. Were going to give it a shot.
     
  7. hrc200x

    hrc200x Active Member

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    Do you have any air leaks between the carb and head? Can be found if bike is idleing and spraying starting fluid around where the 90 degree intake pipe meets the head and carb, listen for a change in RPM. Only thing to watch out for if your needing a air box also is the '79 and newer have a tube going to them for emissions, chances of coming across one of those shouldn't be a issue as they wern't as common as the earlier ones. What are your plans for the old carb?
     
  8. Turbottt10

    Turbottt10 New Member

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    Very large hand held sledge hammer, multiple blows should do it in and make me feel a lot better. I feel better already. I have a keihin pb36a. When I got it a Chinese rebuild kit was already installed wrong and missing parts. If it had all the oem pieces I would just keep playing with it.
     
  9. Turbottt10

    Turbottt10 New Member

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    I purchased a keyster kh-1167n rebuild kit, a new oem float. The needle in this kit is not for my carb.2nd Something is screwed with the slide/ needle if u turn the air idle screw all the way in it does not contact the slide, u can play with the mixture and it varies nothing. Without having a base line to start with it's pretty tough to pinpoint the issues and with parts as they are I just think it's better to start new. I believe chp sells a honda carb for this application, but if its non adjustable, plastic float one setting for the needle I'm really not interested.
     
  10. hrc200x

    hrc200x Active Member

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    Its tough to try and make somthing work when it isnt correct to begin with so a replacement. If it isnt too late and the carb isnt in pieces or the garbage, I'd be interested in it and see if I could get it working.
     
    allenp42 likes this.
  11. allenp42

    allenp42 Active Member

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  12. dirtbkr188

    dirtbkr188 Active Member

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    TBparts.com does have an aftermarket carb for the KO-'77 available HERE, along with a wide assortment of replacement parts and jets for it HERE.
     
  13. Turbottt10

    Turbottt10 New Member

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    Thanks for all the help. As far as old carb it's still together and as complete as it was when I purchased bike. I'm not ready to let go of it yet. But if I do hrc200x I'll send u a message.
     
  14. allenp42

    allenp42 Active Member

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    I doubt this is what you want, but I have a partial china clone version of what I think is PB36a (new) where someone removed the slow speed jet and carb bowl gasket. Everything else is there as far as I can tell. Has a #65 main jet. Will send it to you cheap if it would help you.
     

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