New guy with a 70 CT70, carb questions

Discussion in 'General' started by Norton, Nov 8, 2019.

  1. Norton

    Norton New Member

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    Hello all, thanks for the opportunity.

    I will be workimg on a 70CT for a friend, its got a different carb and manifold, carb is from a honda twin, either 160cc or 175cc marked "680A" as seen in the pics.
    I dont know yet if the jets or clogged but my buddy has said things which lead me to believe it may be jetter too fat.
    He pulled out the main, which he said says "100" but this may or may not be accurate.
    Nevertheless, any idea what would be acceptable jetting for sound performance and dependability on a stock low mile 1970 CT with this carb?

    Thank you.
     

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  3. racerx

    racerx Administrator
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    No one can give you specific jetting guidelines for this carb, fitted to a CT70 engine. AFAIK, it's a one-off...which means it's a "roll-your-own" proposition, IOW has to be jetted & tuned from scratch. That should be possible, as long as the carb was originally feeding no more than ~90cc and the requisite jet sizes are available.

    Pretty cool intake, looks a vintage Webco. Bit of a shame that someone hacked one of the flange holes.:(

    If this were mine, I'd check parts support for this carb. If that's not up-to-snuff, it'd make more sense to just source a new carb and there are plenty of choices out there: new reproduction, OEM aftermarket (service replacement/OER), non-OEM aftermarket such as Mikuni and various low-dollar Chinese carbs. This engine, stock, came fitted with a 16mm Keihin carb. And, rebuildable originals are out there, too.
     
  4. Norton

    Norton New Member

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    Thanks Racerx

    I likely will propose a new carb, this guy is cheap as ****, so we may end up with a chineese knock off, or something like that.
    Within that family, best choices?
     
  5. racerx

    racerx Administrator
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    Best value, in a plug & play reproduction is the hondatrailbikes carb...imho. I looks exactly like the original, even uses all of the same Keihin parts. Come rebuild time, just order the same parts, or rebuild kit as you would if it were the original Keihin carb.

    If you want to go as cheap as possible, source a pz19 Chinese carb. With that option, you're on your own with the jetting. As for rebuild parts...ummm...just buy a new carb.

    Price difference...about $30
     
  6. Norton

    Norton New Member

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    Thanks Racer
     
  7. hrc200x

    hrc200x Active Member

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    Can you verify the motor vin starts with ct70? That looks similar to a cl70 or sl70 carb, maybe someone dropped in one of those motors and kept that carb? Is the cylinder painted black or sliver? I don't think a cl or sl70 would have had a 100 main jet so this theory is probably unlikely.
     

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