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Thread: Honda 250sx still bogging

  1. #16
    mmiguy2103's Avatar
    mmiguy2103 is offline At The Back Of The Pack Arm chair racerFirst time rider
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    Awesome ides guys let me update to what i have checked etc.

    -Fuel flows perfectly into the carb as i have had the bowl off and checked by pudhing up and down on float. I also have the float height right where it should be.

    -Air way is completely clear as everything is new.

    -exhaust is fully clear

    -Fuel cap has no effect.. on or off.


    Thanks for the compliments on this 250sx.. its was built using all parts. its so clean i dont want to ride it haha

    so anyways i have the stock jetting in this what would you guys think to do.. i did try to change the needle clip both up and down one position and didnt see any change.

    the accelerator upgrade to the 350x make sense to me. so i agree it seems like its way lean when i punch the throttle. how can i fix this ? I remember getting the same model 3 wheeler brand new when i was 14 years old and i never had this issue ever with it bogging and dying like this



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  2. #17
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    mmiguy2103 is offline At The Back Of The Pack Arm chair racerFirst time rider
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    Quote Originally Posted by ps2fixer View Post
    That machine really did turn out nice, best 200x front end conversion I've seen, it actually looks natural on the machine. I might have to copy the parts list you use =).
    Thanks alot! i always hated the ugly front fender on the 200x. it was just to wide and stubby. the 250r fender works perfect and give it a way sportier look.. and the 350x headlights... i mean they just look badass lol



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  3. #18
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    Yea, most of the 200x front ends I've seen just look off to me, might just be the 200x fender/light or something. I have plans for building a 250sx frame up but using almost no 250sx parts lol. Longer swing arm, 350cc engine, 200x, 250r, or 350x front end. I have a long long ways to go, but I have the frame and some basic parts. Won't be a pretty build, it's going to be a rider and I'll be riding it hard if/when I finish it =). End goal is effectively a shaft drive 350x.

    I haven't followed the 250es/sx carb upgrade options much, but I suspect a 300ex might be an option, or maybe some newer 250cc quad before EFI was introduced. Intake size, air box size, and length are the major things to try to match up. Venturi size should match the performance of the machine, if it is otherwise stock, I'd target keeping it as close as possible to the stock size.

    I'm interested to seeing the ideas that pop up in this thread, maybe I've just been living under a rock and my machines all need some carb work lol. I don't have any problems riding fast and hard with the carbs I have, but I don't stab the throttle as fast as possible either and under normal riding, I never notice any bogging. I can't recall if the machines will completely stall if jabbed really fast, but I do know they stumble a bit.

    Here's a video I found about the accelerator pump. Little hard to understand him, could use CC to get an idea what he's saying. This is how I understand the situation as well. Also, this is from the era when you'd pump the throttle for starting a cold engine (extra fuel). The people pumping the throttle with an EFI engine don't understand how things work and could be flooding the engine. EFI systems also have a "clear flood" mode, if you floor the throttle and crank, the fuel injectors are not fired and helps dry the cylinder and spark plug, same logic with a carb, but a little gas is still getting in the engine, but the vacuum is so low it's very lean or "dry".

    Last edited by ps2fixer; 03-28-2020 at 07:26 PM.

  4. #19
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    Quote Originally Posted by mmiguy2103 View Post
    Awesome ides guys let me update to what i have checked etc.

    -Fuel flows perfectly into the carb as i have had the bowl off and checked by pudhing up and down on float. I also have the float height right where it should be.

    -Air way is completely clear as everything is new.

    -exhaust is fully clear

    -Fuel cap has no effect.. on or off.


    Thanks for the compliments on this 250sx.. its was built using all parts. its so clean i dont want to ride it haha

    so anyways i have the stock jetting in this what would you guys think to do.. i did try to change the needle clip both up and down one position and didnt see any change.

    the accelerator upgrade to the 350x make sense to me. so i agree it seems like its way lean when i punch the throttle. how can i fix this ? I remember getting the same model 3 wheeler brand new when i was 14 years old and i never had this issue ever with it bogging and dying like this
    Try tapping your CDI with the plastic end of a long screw driver while you are trying to rev it. I say tap, a pretty good hit.
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  5. #20
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    Quote Originally Posted by mmiguy2103 View Post
    Awesome ides guys let me update to what i have checked etc.

    -Fuel flows perfectly into the carb as i have had the bowl off and checked by pudhing up and down on float. I also have the float height right where it should be.

    -Air way is completely clear as everything is new.

    -exhaust is fully clear

    -Fuel cap has no effect.. on or off.


    Thanks for the compliments on this 250sx.. its was built using all parts. its so clean i dont want to ride it haha

    so anyways i have the stock jetting in this what would you guys think to do.. i did try to change the needle clip both up and down one position and didnt see any change.

    the accelerator upgrade to the 350x make sense to me. so i agree it seems like its way lean when i punch the throttle. how can i fix this ? I remember getting the same model 3 wheeler brand new when i was 14 years old and i never had this issue ever with it bogging and dying like this
    Try tapping your CDI with the plastic end of a long screw driver while you are trying to rev it. I say tap, a pretty good hit.
    Feedback for yaegerb: Click Here

    Need something blasted or polished or both? Send me a PM

  6. #21
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    If it runs and responds perfectly normal with the choke on, then you definitely have a mixture/jetting issue.

    Not sure why you're stabbing the throttle so quickly; they can't usually richen quick enough for those throttle settings.

    Do you have another carb to try? Would help in troubleshooting.

  7. #22
    mmiguy2103's Avatar
    mmiguy2103 is offline At The Back Of The Pack Arm chair racerFirst time rider
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    Quote Originally Posted by Baba Yaga View Post
    If it runs and responds perfectly normal with the choke on, then you definitely have a mixture/jetting issue.

    Not sure why you're stabbing the throttle so quickly; they can't usually richen quick enough for those throttle settings.

    Do you have another carb to try? Would help in troubleshooting.
    I have been riding for 30 years.. 100's of different machines. I have never not been able to punch the throttle. There shouldn't be any bogging like I am having. A bog like that can cause accidents. And like I have stated before I had a brand new off the show room floor 250sx when I was a kid and it never bogged no matter how you drove it in any condition..

    And no I dont have a other carb to try



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  8. #23
    mmiguy2103's Avatar
    mmiguy2103 is offline At The Back Of The Pack Arm chair racerFirst time rider
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    I will try tapping cdi box and wiring just to rule it out, before I reinstalled the wiring harness I had made sure to check resistance of every circuit to make sure the harness is good



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  9. #24
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    This is a common problem with the QA series carbs. I have investigated this problem for a long time and I have yet to come up with the cause. Most QA series carbs do this in varying degrees meaning some will completely stall when the throttle is stabbed off idle and some will just stutter. I have take several carbs with this problem and replaced one part at a time and nothing affected the problem leading me to believe the problem is in the body. What Ive been telling guys is not to stab the throttle right off idle. Give it gas and once the motor gets going then hit it so until somebody can figure out what the hell is causing it then that's all we can do. My carb even does that. The QB series carbs which is the same basic carb but Honda added an accelerator pump so I'm thinking its a design problem but that doesn't explain why some carbs don't do it.

  10. #25
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    Some have suggested when the throttle is stabbed the carb goes lean but I disagree with that assessment. I am more in the thinking the problem is a vacuum block. Also, the ES and SX carbs have a primary jet whereas the 350X and TRX250 carbs don't. I have tried the TRX carbs on my test stand with mixed results but the last one I ran had no stall whatsoever. I was laying in bed last night thinking about this problem and I wonder if the primary jet might be causing the problem or at least contributing to it. I need to look through my carbs to see if I have a TRX carb so see if a different carb would have the same results as the last one. Also, I want to put together a carb from a body that I know has the stall problem and block off the primary jet to see what I get.

  11. #26
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    That info I stated is based on what my dad has told me which is was an ASE certified automotive tech (he grew up working on carb'ed vehicles). Either case, I'm interested to see what you can find.

    So what exactly do you mean by vacuum block? When you go at low rpm and open the carb wide open, the venturi has very little air pressure drop across it which causes a lack of fuel flow atleast as how I understand it. Solution is an accelerator pump to off set the fuel demand for those situations. I think another option is a smaller venturi size but then you're limiting max rpm performance (more restricted intake). From my understanding, that's why cars have check valve/one way valve on the vacuum line going to the brake booster, so it can maintain the highest vacuum possible for the most braking assistance.

    Here's a vacuum gauge on an EFI car engine to visualize, never used one but I kind of want one now lol. You can hear that engine bogs a little before taking off too.

    https://youtube.com/watch?v=SdlNwm8OHco&t=223

    Anyway, I'm not trying to argue or anything, I truly want to learn from this, rather me being right or not isn't my focus, just trying to present it as I understand it.

  12. #27
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    If you look at the physics of what happens when the motor goes from a steady idle to wide open throttle in less than a half second I come up with vacuum block. It leads me to believe the sudden burst of vacuum prevents fuel from being pulled from the bowl. I don't know, something is strange about this problem.

  13. #28
    mmiguy2103's Avatar
    mmiguy2103 is offline At The Back Of The Pack Arm chair racerFirst time rider
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    again really appreciate all you guys giving your ideas and what not.. I am a grad from MMI in Florida and worked in a shop for 6 years and it give me a headache thinking about it haha

    I am kind curious to see what would happen by swapping in a 350x carb into it with the stock 250sx jets. i can source a used carb locally for about $100. i might try that after this whole virus world coming to an end things stops lol

    So obviosly its a totally different machine. but i have a 06 suzuki drz400s and it had a CV style carb in it . i had basically the same kind of bogg when i would snap to full throttle but it never would die it would just hesitate. then i swapped out and put in a 39mm FCR mx carb with a accell pump.. and OMG BOG GONE and it Ripped!



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  14. #29
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    I'm not sure how much things are effected by the venturi size, you'd be going from 27mm to 31mm. Also the jetting probably won't work using the 250sx jets, I'd think you'd be better to start with the 350x stock jets if my thinking is right (never done a carb size swap like this). Both of my 350x's do the same thing, so doubt you'll get the benefit you're looking for. The 400ex carb is 38mm venturi but has the accelerator pump.


    I have a table of carb numbers in a table at the link below. The QA series carb is the 250sx/es and 350x type. The 400ex type is the QB series. Maybe a carb from one of those machines would be more ideal like the 91-92 TRX250X or the TRX300EX carbs. I'd personally go for the 300ex ones since they are much newer and made for a much longer time, should be tons of parts on the market and most/all parts available from Honda yet. Took a quick peek on bike bandit and the 2009 version of the QB 300X carb is all available including it as a whole unit for $273.

    https://atvmanual.com/honda/atv-oem-...identification

  15. #30
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    Quote Originally Posted by mmiguy2103 View Post
    I have been riding for 30 years.. 100's of different machines. I have never not been able to punch the throttle. There shouldn't be any bogging like I am having. A bog like that can cause accidents. And like I have stated before I had a brand new off the show room floor 250sx when I was a kid and it never bogged no matter how you drove it in any condition..

    And no I dont have a other carb to try
    Don't need your resume, just trying to help. I have 15 trikes and none of them have instantaneous throttle response. But if it bogs with even moderate throttle application, that is an issue. Your issue is nothing to do with CDI.

    If I were you, I would take it to a bike mechanic that knows carbs well.

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