Help with fine tunning needed.

Discussion in '2-Stroke Engines' started by FelipeCobu, Oct 13, 2013.

  1. FelipeCobu

    FelipeCobu Member

    Hello,

    I'm finishing the tunning of my motorized bicycle after converting it to reed valve.

    Follows the specs:

    Happy Time engine 66cc.
    Converted to reed valve using AV-10 (Motobekane) two petal reed valva.
    I'm using the normal NT Carburetor.
    Main Jet .75 (.75mm)
    Using Castrol Mineral Oil.
    Using 30:1 Gas/Oil Ratio.
    I live at 3000 Ft. Altitude.
    Already set the carb float properly.

    The Simptons the bike is presenting is some sort of sputtering on WOT.

    Follows a pic of converstion and some plugs after running a few minutes:

    2013-10-07 21.00.05.jpg 2013-10-13 21.41.20.jpg

    Thansk a lot!

    Felipe Cobu
     

  2. ddesens

    ddesens Member

    To me the plugs look lean. I think you need to richen up the mixture a little more.
     
  3. crassius

    crassius Well-Known Member

    that intake looks really long - you might be shaking the carb enough to cause the fuel to foam in the bowl
     
  4. FelipeCobu

    FelipeCobu Member

    Agreed dude already choped 3/4 of an inch of it.
     
  5. FelipeCobu

    FelipeCobu Member

    Molded it using poxy putty than send to be casted on aluminun.
     
  6. FelipeCobu

    FelipeCobu Member


    Pics don't show but I'm not using the stock muff, and by my guess CDI has not much to see with engine being able to breath...
     
  7. FelipeCobu

    FelipeCobu Member

    No no, since I'm not a native speaker/write of english it may be hard to understand (things I write).

    I firstly made a piece of resign then I send this piece to be sand casted on aluminum, this last part is what you see bolted to the cylinder in the engine.
     
  8. FelipeCobu

    FelipeCobu Member

    Will increase the jet size on the carb see it stop sputtering and then yeah floor it!

    By floor do you mean run it hard is that?
     
  9. Uncle B

    Uncle B New Member

    Aren't the intake and exhaust swapped?
     
  10. lazylightning@mail.r

    lazylightning@mail.r Active Member

    Hi! You have to keepthat carbuerator level! If it will be leaning to one side or the other it could become very lean. I had the same problem.

    Also, I had a problem with my stock NT carb. The fuel flow was restricted by a very small hole just before the float close off valve. After driving at WOT for a while, the gas in the carb would run out quickly, it would begin to sputter and die. I had to drill out the opening to a 1.5 mm size. Then I aslo had to refinish the mating surface where the float bowl valve closes that opening. I recommend that you first make that carbuerator always stand level. No crooked carbs. If it has a float bowl, then it can begin to open badly and you will not have enough gas to run at WOT correctly and it will be running to lean at high rpm - danger!
     
  11. lazylightning@mail.r

    lazylightning@mail.r Active Member

    Are you joking? He had to turn the cylinder and the piston to face the other direction %-D
     
  12. FelipeCobu

    FelipeCobu Member

    No problem dude.

    And you was right when you say that the engine cant't breath. The reason was not the muffler nor the carb, when I converted the engine to reed valve I done a small hole timed right after the transfer ports closure. Occurs that the hole was too small. Today I dissablemded the whole thing and increase this hole to the size of the intake port. (Sorry my phone was with no battery so can't take any pics.

    Had time for just a test ride, but finally got the bike running well on open throtle, still rich becausethe jetting I done while troubleshooting that issue, but changed like night and day.

    Felipe Cobu
     
  13. HeadSmess

    HeadSmess Well-Known Member

    it wasnt til the 2nd page that anyone realised the cylinder has been rotated?

    mount the carb ON THE REED BLOCK.

    adding any length to the intake just increases the amount of air moving. more=more. more mass=more momentum. you just get reversion waves happening again, defeating the whole purpose of the reeds...



    how well have you matched the transfers? cause they arent lining up too well from the looks of it.

    no point getting the max air into the crankcase if it cant transfer to the cylinder.


    back to the manifold.

    you machined a lump of resin as a mould. why not just machine the lump of alloy? that was the question. a lot cheaper! or route it so the carb is mounted neatly?

    if you went to the effort of casting up the block...why not get a cylinder recast with correct transfers and the rotated exhaust/intake? with an inbuilt reed valve manifold? theres a large demand ;)

    just a thought.

    you did well though. noone else has a pic of a rotated HT cylinder :)
     
  14. FelipeCobu

    FelipeCobu Member

    it wasnt til the 2nd page that anyone realised the cylinder has been rotated?

    mount the carb ON THE REED BLOCK.

    adding any length to the intake just increases the amount of air moving. more=more. more mass=more momentum. you just get reversion waves happening again, defeating the whole purpose of the reeds...

    >>> Yeap that is true. The poing from where the picture was taken make seems that the intake is longer than it really are. I have to made it that way due to space restrictions.


    how well have you matched the transfers? cause they arent lining up too well from the looks of it.

    >>> Externally it may look that way, internally they are, I've also made some porting/ debburing the casting marks too.

    no point getting the max air into the crankcase if it cant transfer to the cylinder.

    >>> I can see you point, and again you're right.


    back to the manifold.

    you machined a lump of resin as a mould. why not just machine the lump of alloy? that was the question. a lot cheaper! or route it so the carb is mounted neatly?

    >>> Because I live in Brazil wich is a under developed country dude, all machining tool I have access is a drill press. So I hand esculped a reging block thand sent to be sand casted on aluminun, way much cheaper around here than machining a billet.

    if you went to the effort of casting up the block...why not get a cylinder recast with correct transfers and the rotated exhaust/intake? with an inbuilt reed valve manifold? theres a large demand

    Cz I'm a hobbist dude. No comparison between casting a "o" shaped block and a new cylinder liner.
    Apples ans Oranges. Also If I o so I will need to found someone do platte it with nickasil or chrome, again to much $$$ involved.


    just a thought.

    you did well though. noone else has a pic of a rotated HT cylinder

    Thanks appreciated that.

    [ ]

    Best regards!!!
     
  15. FelipeCobu

    FelipeCobu Member

    I'm a little concerned about the pistong bearing sideplay, I could see by the marks on the piston pin that the bearing is going sideways.
    I'll ask someone to do me a set of nylon and brass shims, if using the brass shims the vibration is worse will use nylon ones and vice versa.
    I'm thinking too about a boost bootle, and perhaps running it on alcohol since whe have etanol here in every gas stations around here in Brazil.

    Thks.

    Felipe Cobu
     
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