CT70 88cc upgrade

Discussion in 'General' started by Grifter, Apr 10, 2019.

  1. Grifter

    Grifter New Member

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    I’m fitting a big bore 88cc cylinder to my 1978 CT70, does this mean I also have to fit a carb for a 90cc bike?
    And then does that mean I need to upgrade the inlet manifold?
    Also I’ve heard that maybe a high output oil pump would be required?
    Are all these things absolutely necessary?
    I would really appreciate your feedback.
    What seemed like a simple task seems to have grown somewhat!
     
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  3. lukelaw1

    lukelaw1 Active Member

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    Welcome aboard.

    Check out this thread it will give you some great info.
    https://lilhonda.com/index.php?threads/first-time-adding-displacement.14697/page-10#post-138073

    What are you wanting out of the bike? More power, more speed, or just freshen up the cylinder and piston?

    With an 88cc big bore you can usually get by with the stock carb and step up the main jet 1 or 2 sizes, that way the intake can stay the same. Ditch the factory air cleaner for an aftermarket or at a minimum take off the inlet boot.

    A high output oil pump is defiantly a good idea, along with a new HD clutch pack, and a hotter cam.
     
  4. kirrbby

    kirrbby Well-Known Member

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    Welcome to lilHonda Grifter.
    You will likely find some good info in the thread that lukelaw linked...good advice from folks who know.
    I think you could just tweak your stock carb to work fine with 88cc's...including the stock intake. Then decide if you want to upgrade from there. You might squeak a little more performance out of it with a slightly bigger carb. But its never as easy as it seems.

    Whatever size main jet you have right now, buy the next bigger size...or 2. Then swap in the bigger jet before you install the carb and see how your plug looks after you get it running.

    The oil pump is recommended, but if the stock pump is working as it should, it's fine to leave it alone.
    Make it easy on yourself for now.

    What you SHOULD do, is clean the oil spinner. Replace the timing chain, plus any worn gears/idlers. And consider having the head rebuilt...if it's due, while you have it off. The head is more important than the cylinder for a good running CT70. At a minimum...adjust the valves to spec before your first startup.
     
  5. Grifter

    Grifter New Member

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    Thanks for your info
     
  6. Gary

    Gary Active Member

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    I have an 85 kit on my H motor, hotter cam,HD oil pump,HD clutch springs,stock carb,stock head,stock exhaust with baffle removed. Don't remember the jet size but runs a tad rich. Was a California bike so I don't know what elevation it was at but is now in Illinois at around 750 feet. Very happy with how it runs
     
  7. Grifter

    Grifter New Member

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    Thanks Kirrbby..
    Do you think it’s not absolutely necessary to change the cam considering the bike is going to get very little use?
    Also what exactly is the oil spinner?
     

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