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Thread: Honda 250sx still bogging

  1. #31
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    Quote Originally Posted by mmiguy2103 View Post
    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!

    Did this carb bog like this before you took it apart?
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  2. #32
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    Have read that needles have different tapers just wondering if a different taper might change things. Also the ramp on the slide?? Thinking outside the box Also the frame tubes to air box you might run some stiff wire just to verify that there is no obstruction even after all you’ve done
    you know whats right therefore you know what is expected

  3. #33
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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 yaegerb View Post
    Did this carb bog like this before you took it apart?
    oh yes this was a problem for a long time



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  4. #34
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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 danbur55 View Post
    Have read that needles have different tapers just wondering if a different taper might change things. Also the ramp on the slide?? Thinking outside the box Also the frame tubes to air box you might run some stiff wire just to verify that there is no obstruction even after all you’ve done
    i have verified that the entire intake even through the frame is open and flowing perfect. thanks for the idea! yes needles have different tapers.. I am using all the stock jets and jet needle. all new from Honda verified. everything is stock and i am at about 50 FT Above sea level.



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  5. #35
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    The carburetor bodies are a cast piece, that requires machining to finish. The fuel and air circuits are drilled into the carb body, and the ones drilled through or from the outside, require a plug to seal the passage. These are the things that look like little brass BBs.

    That carburetor was a mass produced item, made over thirty years ago. Those plugs can loose their seal, or may be they never had a good one to start with and it just got worse.

    This is an actual problem on other carburetors. Some are known for it, while it's seldom a problem on others, but any carburetor with presses in plugs can develop a leak there.

    A hanging idle that you can't get rid of could be a symptom of it, if the idle circuit is sucking in air. That would be the little BB on the very end of the carb on the engine side.



    The quickest fix is usually a dab of epoxy over the offending seal. In this application, I think a dab of clear fingernail polish would actually work, and I'd put it over all of the sealed passages on the outside.

    That's simple, inexpensive, and if done cleanly, it won't be noticeable.



    The other thing I'd do, is check the valve clearance again.
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  6. #36
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    I never thought about those plugs leaking, I bet you're onto something there.

  7. #37
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    You could be on to something "The Mr. King"
    I have a factory carb Keilin on my 200m, I cleaned it 3 times, I put every component of a Shindy rebuild kit into it. and it still did the same thing. wouldn't idle, hanging idle also.
    Just when I thought I figured it out it acted up again. I tried everything richer/ leaner etc, etc.
    I cleaned and rebuilt a different OE carb the same way I have always done it, and put it on, The bike runs perfect now, no hanging idle, it idles great now.

    So, do you have another carb to swap just to rule out a few things?
    Even an ebay carb would eliminate some things like , ignition, timing, leaks, intake ect.
    Why not do the upgrade to the 300ex/400ex carb as a test, you may like it.

    MrC.

  8. #38
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    My .02....if everything else checks out I would think the carb is still suspect. The hanging idle is what leads me to believe it’s truly carb related. You can clean up a hanging idle be richening or leaning the idle circuit. Honestly at this point I would get a different OEM carb and rebuild it. Especially since you had this problem before disassembly.
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  9. #39
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    I am sending MMIGUY a Chinese carb I bought years ago that runs great. This carb is an 86/87 clone and when I got it, there were a few minor discrepancies but its always ran good. I asked Chris if he would send back his carb and I am going to explore the sealing ball suggestion made by ATC King to see if it makes any difference. That's one thing I never thought of. Over the years people have asked a lot of questions about my test stand so here is my very first You Tube upload of the test of the Chinese carb for you motor heads. This test stand has been an invaluable tool for me over the years. https://www.youtube.com/watch?v=YGnuNSzyfr4

  10. #40
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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 Flyingw View Post
    I am sending MMIGUY a Chinese carb I bought years ago that runs great. This carb is an 86/87 clone and when I got it, there were a few minor discrepancies but its always ran good. I asked Chris if he would send back his carb and I am going to explore the sealing ball suggestion made by ATC King to see if it makes any difference. That's one thing I never thought of. Over the years people have asked a lot of questions about my test stand so here is my very first You Tube upload of the test of the Chinese carb for you motor heads. This test stand has been an invaluable tool for me over the years. https://www.youtube.com/watch?v=YGnuNSzyfr4
    again thanks so much!! i am excited to see what this chinese clone will do!



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  11. #41
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    Neat setup for the test bench, thanks for sharing. I originally thought you legit installed the carbs on a 250sx/es machine as a whole. Since this is a true "bench test" type of setup, one upgrade I could see is going for an exhaust gas analyzer and/or O2 sensor and a tach that's a bit more responsive.

    I think the bog is most noticeable from idle and flooring it. Mid to max haven't really had bog problems. I'm only able to really bog my engines by basically slapping the throttle to go from 0% throttle to 100% almost instantly, like normal riding position I might get a tiny bit of a bog but nothing to even bother with. Only exception is one machine I have that has a minor bog problem and the idle hunts a little, so really interested in what we can find out in this thread =).


    Personally, I think the O2 sensor setup with a fast responsive voltage meter (one that doesn't average over time ideally for quick response) would give good tuning experience besides by ear like the video below. This is for a car/truck engine, not sure how well one would work on a small atv engine. Could look into what the EFI style atv's run and try one of their sensors. More wires just means it has a heater to get to closed loop faster. Clearly not the typical setup for the average person.

    Now I want to look into O2 sensors a bit more and see what the distance requirements are from the engine that they work well at. Maybe the exhaust flange location could be used as a temp hookup with a short adapter between exhaust and head pipe to tune the carb. It's a pretty standard interface so it could be somewhat universal for any Honda atv.





    My dad has one of the sun engine testers like the big one in this video, don't know much about it but he has to replace all the vacuum hoses on it and re-calibrate it. He's had it for atleast 20 years that I know of. It's like from the 60's era if I'm thinking right. He wants to fix it up because he's been getting into building chain saw engines up and wants to tune besides ear and rpm to make sure he's doing it right. Too lean on a chain saw is a bad mistake. I'd like to use it for atv engines and such =).

    https://youtube.com/watch?v=lEDMuzj4GKM&t=83

  12. #42
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    The tach I have is inductive and all I use it for is setting the idle speed so it works just fine for the way I use it. As you can see, the setup is exactly as it is in the frame. Stock airbox, stock muffler, and a cut down electrical system. Whats cool about this setup is I mounted it to the top of a Harbor Freight 5 drawer toolbox. I didn't want to lose the storage area under the lid so I installed four linear actuators and a 12v battery so when I need access to the tools under the lid, I hit a switch and the whole thing rises up 10". I put tools under the lid I rarely use so I'm not in to it too often.

  13. #43
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    Here's my second YouTube video upload of how I raise the lid. https://www.youtube.com/watch?v=Z7IMxK5F87E

  14. #44
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    That's quite a setup now. What do you do about say a 350x carb when you rebuild one of those? Test it on the same engine?

    Those actuators don't sound too happy with the weight, but they work =). I wonder if adding long enough struts to it would help take some of the load off them. Probably not worth doing, as the saying goes, if it's not broken, don't' fix it.

    I need to get further with my CDI research stuff, I suspect you'd probably be one of the people that would benefit from something like that (able to test most/any Honda CDI).

  15. #45
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    Each actuator is capable of lifting 300lbs so there is 1200lbs of lifting power there. I test the 350X carbs the same way and I don't have to make any changes to the test stand.

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