Past the power curve ?

Discussion in 'Motorized Bicycle General Discussion' started by rob king, Nov 19, 2009.

  1. rob king

    rob king New Member

    Joined:
    Oct 13, 2009
    Messages:
    8
    Likes Received:
    0
    I've got a stinger sd"80cc" motor on my board tracker. Have run about a gallon of gas through it @16 to 1.I just swithched to synthetic motorcycle racing oil @ 50 to 1. Engine makes real good power under load but when bike is atwide open throttle and cruising ti kind of fallsoff and surges . throttleback and put load on it pulls hard again. I have 44 tooth sprocket. Should I goto a smaller rearsprocket to keep it in the power band better. My friends bike with 80cc slanthead motor and I think36 tooth rear sprocket seems to pull all the time even at cruise wide/open. Plug is fresh ngk and nicegrey/tan color after hard run. Anythoughts
     
  2. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

    Joined:
    Mar 20, 2008
    Messages:
    6,228
    Likes Received:
    32
    Re-jetting the carb a hair smaller has always fixed this problem for my bikes! ;)
     
  3. captainrichhill

    captainrichhill New Member

    Joined:
    May 31, 2008
    Messages:
    203
    Likes Received:
    0
    Ditto! Same for me.
     
  4. fall_down_stand_up

    fall_down_stand_up New Member

    Joined:
    Apr 26, 2009
    Messages:
    555
    Likes Received:
    0
    What size drill bit would I use to do this????Resoder it and then redrill the hole????I think I will just wait until SBP gets there carbs back in stock....
    John-John
     
  5. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

    Joined:
    Mar 20, 2008
    Messages:
    6,228
    Likes Received:
    32
    Just go to a hardware store that sells tiny 'jewlers' bits; find the one that fits in your jet perfectly, & then buy the next two smaller sizes!! I think #70 is what the stock jet is??
     
  6. BarelyAWake

    BarelyAWake New Member

    Joined:
    Jul 21, 2009
    Messages:
    7,209
    Likes Received:
    5
    Another thing to check/try is bending the float tabs up a hair - could be just a starvation issue... It was with mine anyway ;)
     
  7. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

    Joined:
    Jan 8, 2008
    Messages:
    11,529
    Likes Received:
    4
    ....or a loose jet.

    #70 is .028"
    #71 is .026"
    #72 is .025"

    I got a whole set off of ebay for 6.99 shipped.
     
  8. Kevron99

    Kevron99 New Member

    Joined:
    Aug 11, 2009
    Messages:
    261
    Likes Received:
    0
    Spooky will have the CNC Carbs on day after thanksgiving.
     
  9. rob king

    rob king New Member

    Joined:
    Oct 13, 2009
    Messages:
    8
    Likes Received:
    0
    Ive tried your suggestions about going to smaller jet size . my original was in between #70 and # 71. TI have a metal lathe and can make my own jets ,wanted to save the original intacked. went down .004" problem seems a slight bit better but much. I'm not sure this thing is fukky broken in yet, I'm going to run it more and see what happens. even after going down in jet size plug still looks just a touch rich. How long does it take to fully break in one of theses motors? thanks for all the help. I'm stuborn and wont quit until it runs right!
     
  10. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

    Joined:
    Mar 20, 2008
    Messages:
    6,228
    Likes Received:
    32

    Don't try to re-jet your carb until you've fully broken in the engine!!! (about 4 gallons!)
    It will start running different as it breaks in! (& you'll have to re-jet again)
     
  11. rob king

    rob king New Member

    Joined:
    Oct 13, 2009
    Messages:
    8
    Likes Received:
    0
    First let me apologize for my spelling errors. hard enough to get your thoughts across without all the mispelled words! I found a problem that may not be that unusual but caught me. Even after trying rejetting with no noticeable change, I got to thinking about what else could be at falt. New motor and all I new it probably won"t run as well as a well broke in engine, but I knew something was definately wrong. Still surging at cruise speed. Pulled bike into the shop and sat there just reving it a few times when I saw the carb moving! Intake bolts were loose. Funny cause they were tighten with wrench yesterday. Come to find out, factory installed acorn nuts were bottomed out on studs. felt tight but no pressure on intake manifold.so it was wiggling and allowing intake to leak.any one seen this one before? for such a simple engine, look for the simple problem! got rid of acorn nuts and put regular nuts with lock washers. anyway it runs much better now and i'm sure will run better as it breaks in more. I put original jet back in and will run it like this for awhile .thanks again for all help
     
  12. sportscarpat

    sportscarpat Bonneville Bomber the Salt Flat record breaker

    Joined:
    Jun 25, 2009
    Messages:
    1,752
    Likes Received:
    66
    I have seen the bottomed out acorn nut issue and changed mine out as well. I also suffered from high rpm fuel starvation. Drilled out the lower fuel petcock and put in a larger fuel filter. The guy at the lawn mower shop told me to always use the metal screen type filters for gravity feed applications. Paper type filters will not flow enough fuel. Problems solved and I now have plenty of fuel at WOT.
     
  13. spit_fire

    spit_fire New Member

    Joined:
    Aug 28, 2009
    Messages:
    207
    Likes Received:
    0
    i have a question to all the have rejetted with the almost pubic hair size drill bits, do you do it by hand with a hand drill, dremel, or some sort of drill press?
     
  14. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

    Joined:
    Jan 8, 2008
    Messages:
    11,529
    Likes Received:
    4
    A pin vise drill. (hand drill bit holder- looks like a small screwdriver.)
     

Share This Page