XR100ish engine help

Discussion in 'Mini Racing' started by backcountryme, Mar 26, 2012.

  1. backcountryme

    backcountryme Word to your mother.

    Ok, so I got a YSR with a Lifan XR100 clone engine. I have done some work on the bike and have gotten it pretty close to running right. My problem is that it starts fine, idols fine, but when the RPM starts to climb it starts missing. I have checked the carb and it is spotless. I have re-jetted it and now the plug looks nice. Chocolate brown and dry. It really only starts cutting out (almost like a miss) around half throttle and higher, but only after about 3000 RPM. Could it be electrical, or more likely fuel? It doesn't cut out when it is out of gear, only under load. I have the clip on the needle set in the middle, a 92 main jet, 38 pilot jet, and the fuel screw 2 turns out. Oh, I am at 3200 feet. I do have a 95 main jet in my tool box. Any suggestions would help as I am not that great a tuning a carb.
     
  2. ACDNate

    ACDNate Well-Known Member

    I'd try moving the clip on the needle one slot and bump the main jet to that 95. The stock honda carb had a 98 main in it (if memory serves me correctly) and it was pretty lean (at least at sea level, I haven't got a clue how the 3800 feet of altitude affects it)
     
  3. backcountryme

    backcountryme Word to your mother.

    I'll try the needle setting and see what that does. I know that the higher in altitude you are the leaner the main jet needs to be. I am just not to sure where to start. Ha. I think that I'll do the needle first. If that doesn't clean it up then I will do the main. Thanks for the help.
     
  4. raddad13

    raddad13 Well-Known Member

    could be electrical, I had one give me fits last year, all signs pointed to jetting and after jet after jet after jet moved clip around with no luck. I started swaping elc. parts to rule it out and it was my cdi the whole time. like yours mine was at 3/4 to full throttle mostly top end.
     
  5. earacing

    earacing Race Dad

    I'd have to hear what it sounds like to be sure, but our 150 sounded like it was missing at higher RPMs in Vegas, sort of sputtering. Turned out it was too rich.
     
  6. Kurlon

    Kurlon Well-Known Member

    Yeah, try taking the airfilter off, 92 main, drop the needle and see how it does WOT before richening it up at all.
     
  7. backcountryme

    backcountryme Word to your mother.

    I have the stock cdi (I put a high output one on) that I will swap back on. I never even tried it on this engine.
     
  8. blackbird2xx

    blackbird2xx Active Member

    check the coil. I had that happen on my xr100 motor. Raddad13 is a friend of mine, and it was both of our coils. Everbody thought it was our carbs.
     
  9. backcountryme

    backcountryme Word to your mother.

    Ok. I have a known good coil too. I'll try that also. Thanks for all the info everyone. I am fairly new to all this single cylinder stuff. Give me a 370 hp mechanical injected esslinger midget engine and I know what I am doing. Funny how a simple little single has gotten me so confused. Ha
     
  10. ACDNate

    ACDNate Well-Known Member

    I'd give that a shot as well to make sure you don't have a wonky aftermarket cdi. Rule out the easy swap stuff first.
     
  11. turner38

    turner38 Well-Known Member

    Make sure the cam isn't a tooth or three advanced.:D
     
  12. backcountryme

    backcountryme Word to your mother.

    I don't think it is, but I should check that.
     

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