FMF Powercore and Carb Jet
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  1. #1
    Junior Member 737mechanic's Avatar
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    Just installed a Powercore 4 on my 2010 tee dub and am enjoying a pretty noticable increase in midrange power. It seems to idle alright, and for the most part runs ok. However, if the engine goes from a heavy accelleration or 3/4 throttle to full closed (getting off a highway) it blubbers and pops. If you pull the clutch lever in it goes to the idle circuit and seems to correct itself. How can I smooth her out? I reckon I need a little bigger main jet in the carb. It's a Mikuni. I have not modified the intake at all and want to adjust one carb item at a time so I can keep stuff close to being right. Any other thoughts?

  2. #2
    Senior Member RodneyReed's Avatar
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    Quote Originally Posted by MSP Fly Guy View Post
    Just installed a Powercore 4 on my 2010 tee dub and am enjoying a pretty noticable increase in midrange power. It seems to idle alright, and for the most part runs ok. However, if the engine goes from a heavy accelleration or 3/4 throttle to full closed (getting off a highway) it blubbers and pops. If you pull the clutch lever in it goes to the idle circuit and seems to correct itself. How can I smooth her out? I reckon I need a little bigger main jet in the carb. It's a Mikuni. I have not modified the intake at all and want to adjust one carb item at a time so I can keep stuff close to being right. Any other thoughts?


    Sounds like your bike is running lean.



    Qwerty's got it all figured out. See his post below.



    https://tw200forum.com/index.php?/topic/647-carb-tuning/

  3. #3
    Banned qwerty's Avatar
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    One change at a time is the way to go--main, needle, pilot, in that order. You'll have a better tune in less time in the long run.




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  5. #4
    Junior Member 737mechanic's Avatar
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    Thanks for the fast reply all. I confirmed my suspicions and your suggestions about running lean by pulling the plug this morning after I got home from work. It just looks hot and dry. Most plugs are a little more interesting looking. This one just looks well, lean. I have a #130 main jet on order, and will start my adventure into carburetors in 7-10 business days.

  6. #5
    Junior Member 737mechanic's Avatar
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    Just installed the number 130 main jet. It still wants to blubber with a load on the engine and the throttle closed. So do I just get a 132, 134, etc. until the blubber is straightened out? Or is this just the nature of the beast?

  7. #6
    Senior Member pgilles's Avatar
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    Does it blubber while holding it wide open? Or only when you suddenly, quickly close the throttle after wide open? If it runs well at speed but not when you close the throttle immediately after then you may need to richen up the needle & pilot to keep it from blubbering at closed throttle in those conditions. Try shimming the needle some. Then adjust the pilot.
    Sold bike.



    Youtube vids of old TW's acceleration:

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  8. #7
    Junior Member 737mechanic's Avatar
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    No, it runs great wide open. In fact, I think with the mixture more rich with the bigger main jet it runs better than the stock 126 jet. It only blubbers if the throttle is suddenly closed at just about any speed. More notable if at a higher speed when the closing of the throttle occurs. No blubbering as soon as you pull the clutch lever and take the load off the engine. After reading the write up qwerty did on this subject I think I am either going to try a 132 main jet the shim the needle, or is it worthwhile shimming the needle now?

  9. #8
    Senior Member pgilles's Avatar
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    You'll probably find that the main jet will end up being a 130, but you could go trying larger ones to be sure. I'd say shim the needle and adjust the pilot where you are at, if you are satisfied with plug chops and the way its running with your current main.



    It will run better with more fuel, as you found out. Most come lean.
    Sold bike.



    Youtube vids of old TW's acceleration:

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  10. #9
    Senior Member RodneyReed's Avatar
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    I would try shimming the needle first.

  11. #10
    Banned qwerty's Avatar
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    Is everything else right with the bike?



    Occasionally, after a fast stretch of highway and some decel, Tdub will bog at roll-on. Seems to be worse with E10. Seems to be common on TWs.



    If you can tell no performance difference at wide open between the 130 and 132, I'd stick with the 130 and try messing with the needle height next.




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