Inside Diameter of Intake Tube

Discussion in 'General Questions' started by Fast Shag, Nov 10, 2014.

  1. Fast Shag

    Fast Shag Member

    The stock tube that came with my Flying Horse 66cc is 14mm inside Diameter. The speed carb came with the kit. I acquired another no name, used 66cc motor with the NT carb and an intake tube with 17mm inside diameter. I think the NT carb has a 14mm bore, and Speed carb 17mm. Now do these company kits just throw pieces together and ship them off, or do new regs on emissions call for small intakes on 66cc motors? I understand that these motors can only suck up so much air and fuel due to their design, but have any of you seen these new intakes? Obviously I threw the larger intake on my good bike with Speed carb.
    and this is the old one I replaced it with.

    What are your guy's thoughts on this?:thinking:

  2. butre

    butre Well-Known Member

    the smaller intake is a cast one that I think is meant to come with the 48cc, while the larger one is pipe welded together and comes on all the 66cc engines I've had
  3. crassius

    crassius Well-Known Member

    true, the steel one is larger than the aluminum just because steel can have same strength while thinner

    aluminum is less likely to bend out of shape & leak air, while steel will often allow greater flow volume
  4. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    To get maximum flow I made and sell thin wall straight shooter steel intakes.

    My intakes use 3/4" OD tubing which at 19.04 mm is a tight fit on the NT, Speed and RT Carbs.

    The intake tubes are brazed to a 1/4" thick lazer cut flange.
    1 1/2" long overall.

    Yes, aluminum intakes have a thicker wall than steel ones because of material strength.
  5. HeadSmess

    HeadSmess Well-Known Member

    strange.all my 48s had steel intakes,and the 66 had the cast alloy one. and when it broke...did it weld nicely? no. it turned into a spitting lump of molten crud...

    just grind out the flanges to suit the ports, gaskets, and remove the slag at the bend/weld...
  6. Fast Shag

    Fast Shag Member

    NOTE: My new 66cc Flying Horse motor that came with the cast alloy 14mm intake came from Bikeberry. I believe they are cutting corners for the 66cc motor. I don't think it is an issue with the 49cc motor, giving the fact that the NT carb only has a 14mm bore. But having that 14mm intake on a 66cc with a 17mm Speed or racing carb will decrease air/fuel intake, defeating the concept of getting air/fuel in and outta the motor as quickly as possible for maximum performance.

    The reduced form of the corresponding equation relating in terms of variables, arbitrary values, and specific solutions for modulator technology.....
  7. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    The NT carb has a slide diameter of about 14.5 mm
    The Speed carb has a slide diameter of about 15mm
    That would be only 1/2 a mm bigger.

    Been doing motorized bike kits since 2008.
    Your comment about emmision regs is ridiculous,

    48 cc and 66c have come with any mix of steel or aluminum intakes over the
    6 years I have been selling them, it only depends on what the chinese factory
    decides to put on them with no performance reasons whatever.

    I can order my 69cc kits from China with whatever intake I want.

    There is nothing new except you. :)
  8. Fast Shag

    Fast Shag Member

    Thanks for clarifying 15mm size.

    These are questions I ask before you, not statements. Somewhere here on more than one thread I read that they detuned these motors for emission reasons. Guess they were wrong. In your 6 years of mastering the motor bike concept have you found that larger inside diameter intakes help performance, given many other factors?

    Yes, I'm new to this, reading and studying threads, and posting questions that haven't been addressed. You should write a book on all this cool stuff.:evilgrin: Good to see that So Cal attitude is still alive and well. Rock on
    Last edited: Nov 11, 2014
  9. Purple Haze

    Purple Haze Active Member

    These kits are considered "parts" to get around emissions regs. In fact, I've bought kits that had "parts" labeled on the box. Back to the intake question, I think they buy them from different companies "subcontractors" and of course shop for the lowest price, then package them in kits according to what they have on hand that day. As far as performance, a little time spent with a dremel or file cleaning up the welding slag helps quite a bit, but you are limited at the flange due to the bolt spread and weld area. Go too far, and you'll have leaks. Also, making the intake diameter too large kills low-end torque, and can cause reversion, which hurts performance across the board.
    Fast Shag likes this.