Is it a lean surge?
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  1. #1
    Senior Member Guitarman's Avatar
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    Hi everyone!



    When I ride at sustained speed, I sometimes feel like the engine "miss a beat". Is it what is called a lean surge? I've red qwerty's post about carb tuning and he describes it like a quick roll off/on of the throttle, that's what makes me think my problem might be.



    Am I looking in the right direction?



    The only thing I've done to the carb was to add a 130 main jet, shim the needle to 0.03 and open the pilot screw to 2 1/4. It did not cure the lean condition. Spark plug went from snowy white to light grey. I have a stock and clean air box.



    Thank you for your help!

  2. #2
    Senior Member Gerry's Avatar
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    With situations like this, you need to be very 'specific'. Folks can make guesses but likely can provide a great deal more insight if YOU provided more (detailed) information.. I suspect, those that can help you would like to know rpm. I gather per your other posts, you do not have a tach. No problem, let folks know the speed and gear you are at when you experience this "surge".



    My bike has lots of mods. I as well have played with the carb, but it seems the process is not as yet, correct. I get a bit of hesitation/surge around 3800rpm's. I have not raised the needle as much as others, perhaps this is the issue. As I am not asking the question, I will not belabor my 'situation'.



    Guitarman, we likely would profit from more information. Gerry
    Take care my Friend.........

  3. #3
    Senior Member Guitarman's Avatar
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    I'll try to give you as much info as I can, but since it doesn't happen all the time, it's hard for me to be very precise.



    It usually happen when I'm in 5th gear, sustaining a speed between 50-60 mph.



    It seems to be more frequent when I'm climbing a hill, and even more if my girlfriend is on the back.



    Throttle is somewhere between 3/4 (maybe a bit less) and full.



    The "surge" is like a quick miss, I feel pushed forward for a split second (the bike decelerate).



    Is there any other info that could be useful?



    Thanks again!

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  5. #4
    Senior Member jbfla's Avatar
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    A lean surge is a slight speeding up and then slowing down when the throttle is held steady in one position.



    It should happen in any gear, but usually more noticeable at smaller throttle openings.



    With the larger main jet and shims, it shouldn't be lean... unless there is a vacuum leak.



    Your "miss" sounds like something else... but that's just a guess.



    jb
    2018 Triumph Street Twin..............2016 CB500F
    2014 XT250 ..................................2008 H-D Softail Deluxe
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  6. #5
    Senior Member n2o2diver's Avatar
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    My 2005 does the same thing and it is driving me crazy. Always at high rpm when sustained. Doesn't mater if I'm in 4th or 5th. I also have a 130 main, 2 1/2 turns and 3 shims. I'm really starting to think the problem is electrical. Because it is so sudden and of such short duration. Only cuts off for a second then picks right up. I'm open to suggestions but I'm pretty much done with clean the carb or petcock. I have! Again and again! It is a new tank, new petcock, new float needle assembly, new needle, carn is spotless inside and out, ran guitar strings thru every oraface. Bike really runs great other wise. Just cuts out now and then while holding sustained high rpm, I almost thought it was a rev limiter. It was really bad when riding up long highway hills. I'm hoping qwerty might have a suggestion.
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  7. #6
    Senior Member Guitarman's Avatar
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    Quote Originally Posted by n2o2diver View Post
    It was really bad when riding up long highway hills.


    Could it be float related??

  8. #7
    Senior Member Guitarman's Avatar
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    " Engine operating symptoms of a carburetor with a float level too low can be hesitation and inability

    to handle load due to a mixture that is too lean. "



    Taken from Carburetion Troubleshooting

    Quick Reference Guide
    http://www.briggsandstratton.com/sup...nce_guide.ashx

  9. #8
    Senior Member jbfla's Avatar
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    Quote Originally Posted by n2o2diver View Post
    My 2005 does the same thing and it is driving me crazy. Always at high rpm when sustained. Doesn't mater if I'm in 4th or 5th. I also have a 130 main, 2 1/2 turns and 3 shims. I'm really starting to think the problem is electrical. Because it is so sudden and of such short duration. Only cuts off for a second then picks right up. I'm open to suggestions but I'm pretty much done with clean the carb or petcock. I have! Again and again! It is a new tank, new petcock, new float needle assembly, new needle, carn is spotless inside and out, ran guitar strings thru every oraface. Bike really runs great other wise. Just cuts out now and then while holding sustained high rpm, I almost thought it was a rev limiter. It was really bad when riding up long highway hills. I'm hoping qwerty might have a suggestion.
    Hi N2o2,



    I have the exact same carb setup as you on my '05, and regularly ride long uphill stretches in the mountains. There is no hesitation or miss...just a slowing down of speed if the hill is too steep.



    It won't hurt to check the float level.



    I suspect it may be something else, but am not sure what.



    Sorry I can't offer a definitive cure.



    jb
    2018 Triumph Street Twin..............2016 CB500F
    2014 XT250 ..................................2008 H-D Softail Deluxe
    2008 SV 650..................................2007 DR 650..

  10. #9
    Senior Member n2o2diver's Avatar
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    Thanks, I will check the level maybe that is it.
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  11. #10
    Banned qwerty's Avatar
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    I get three guesses, right?



    Spark plug, vacuum leak, float level.




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