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Thread: 250 ES Bogging

  1. #1
    Join Date
    Sep 2011
    Location
    new york
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    50

    250 ES Bogging

    Hi. Picked up a 1985 250 es big red. The issue: if i give it throttle too quickly, it will bog out. Bog out in my case is appears to lose fuel, and want to shut off. it actually will shut off if i hold the throttle open. if i immediately release it, and reapply the throttle slowly, i can “save it” from shutting off. i removed the carb and rebuilt it with a shindy kit. it was actually not that dirty. must of been cleaned by the previous owner. what i did notice, was the air screw was missing the washer, and the rubber o ring was crushed in between the spring....so i thought i def found the problem.. nope... problem still exists. i thought about the synchronization, but it looked good to me.. 2 turns out on the air screw. Original exhaust, and oem air box. new gas, plastic tank, new plug. I removed the exhaust clearing plate, pretty clean, not much carbon crud at all..just need some advice from the veterans as to where to turn next. plug inspection? valve clearance? ignition adjustment? never played with cdi system..Thanks in advance..

    PS: i own a 70 that does the same and could never figure it out..currently down to the frame for overhaul..rings were shot and fouling plugs..

  2. #2
    Join Date
    Apr 2011
    Location
    Mexico
    --
    9,003
    Couple comments...

    Synchronization is a term used to match the vacuum of two or more carburetors on the same engine. Does not apply to your application.

    Usually a four stroke carburetor has a fuel screw, not an air screw. If your screw is located between the carb and cylinder it’s probably a fuel screw. If it’s situated between the carb and the air box it’s an air screw.

    Assuming yours is a fuel screw you can try opening it one full turn to see if that helps. If it does you can try to fine tune it from there.

    I’ve seen a couple Mikunis where someone has over-tightened the fuel screw to the point that the tip broke off in the orifice. That will cause a lean condition from idle to 1/4 throttle.

    Where is the clip on your slide needle located at the moment? Lowering the clip to raise the needle can also help cure a lean condition from 1/4 to 3/4 throttle. If you’re not sure where it should be start in the center position. Some carbs have a small Teflon waster under the clip. If yours uses one and it’s been lost it will cause a lean condition from 1/4 to full throttle.

    Do you have the right plug and gap? Important!

    Make and test your adjustments one at a time or you’ll get unnecessary frustrated.

  3. #3
    Join Date
    Sep 2011
    Location
    new york
    --
    50
    thanks for the reply, familiar with multi-carb sync, however with this carb i was referring to the slide and butterfly sync. i really need to take a second look at this as i didnt spend too much time after the rebuild. i was using flyingw’s amazing carb rebuild post..
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    the screw i was referring to is the pilot screw. between eng and carb so a fuel screw (explains o ring) i set it 2 screws out initially and have gone in and out, same problem. i dont think anything is broken in there because the old one came out intact. i replaced it with a new needle,spring,washer,o-ring..
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    clip position is 2nd groove as per manual. will need to research regarding teflon washer underneath, i believe this keihin carb does not have a teflon washer..
    Click image for larger version. 

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    check and check on the new plug and gap...

    So just to confirm..i believe you suspect an excessively lean condition? i will adjust the clip position and readjust and record the turns of the pilot screw with the new clip position..

  4. #4
    Join Date
    Sep 2011
    Location
    new york
    --
    50
    i will also bog it out, a few times, let it shut off..and then take a pic of the plug as well. thanks for the help..
    PS: since there is no acceleration pump on this carb, what is responsible for ensuring a excessively lean mixture does not occur during rapid acceleration?

  5. #5
    Join Date
    Apr 2011
    Location
    Mexico
    --
    9,003
    You should be able to confirm if the washer, or lack of with a parts fiche. If you’re lucky FlyingW will pop in here.

    No chance you have a cracked or leaking manifold?

  6. #6
    Join Date
    Nov 2019
    Location
    Florida
    --
    1,044
    Does it bog with partial choke applied?
    Does the choke work, meaning does it change how the bike is running if you apply choke? if yes, good otherwise the choke could be stuck/broken letting in air.

    I am no carb expert, but I do use the choke to tune a carb, if with partial choke applied it clears up and does not bog, then its running rich.
    adjusting the air mixture screw or by moving the clip on the needle up will lean it out.
    If it still bogs with the choke on, then I would suspect, the wrong main jet was installed or a plugged circuit.

    MrC.
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  7. #7
    Join Date
    Jul 2009
    Location
    South Florida
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    6,722
    Their are several threads on this problem with the QA series carburetors on the sx & es models , to my knowledge nobody has figured it out yet , not even Jim who is our resident expert .
    My suggestion to you is if you can’t figure it out to simply go on eBay and find a good used OEM carburetor and put the shindy kit in it you just purchased , this will save you a lot of frustrations .

    I would definitely play with the needle setting though first , go extreme each direction and see how it responds .
    78 atc 90/180cc Dickson Full Suspension
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  8. #8
    Join Date
    Jul 2009
    Location
    South Florida
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    6,722
    On the ATC70 , if you are using the factory carburetor ? The factory air box setup needs to be sealed perfectly , without an air box or with an aftermarket filter it will not run properly , it needs that restrictive air flow the factory air box give to run properly .





    Quote Originally Posted by flyingatc View Post
    PS: i own a 70 that does the same and could never figure it out..currently down to the frame for overhaul..rings were shot and fouling plugs..
    78 atc 90/180cc Dickson Full Suspension
    76 ATC90/180cc Nicholson
    77 atc 90 Dickson Full Suspension
    84 KLT 110/123cc Powroll Racer from 80s
    87 atc 125m stock
    84 atc 200x Curtis Sparks
    84 atc 200x Powroll My race bike from 80's
    83 atc70/108cc Powroll blue Xmas Special
    81 atc185s HP-ATC full suspension

    Performance Shop is Open PM me for Service

    My Feedback http://www.3wheelerworld.com/showthr...ck+shortline10

  9. #9
    Join Date
    Sep 2011
    Location
    new york
    --
    50
    Update #1: lol.. Tried throttle-up with with partial choke, still bogs.. choke works well..i actually performed the cold weather mod, so it started pretty quick, but if i leave it choked past warm up it will start running rough. When i release choke, clears up.. so i feel choke is operating normally.. Before i changed clip position i removed air box lid, same bog issue..I looked at spark plug after allowing it to bog and shut-off several times.. looks kind of carbon fouled, couldnt chop due to time..Pics not the best..
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    Next, i moved the clip on the needle, down 2 groves.. so instead of 2nd groove i went to 4th groove, enriching the mixture.. same! Still bogs.. 4th groove went in all the way on pilot needle, almost shutoff(so i know the pilot screw is "working") tried 1, 1.5,2,2.5,3 turns in out etc.. same bogging issue.. i might look at float level next?Although a new carb sounds tempting..Thanks to all who chimed in..
    ps: Re: atc 70 i had Aftermakret carb and oem Airbox.. now i purchased an oem carb, on rebuild will install..
    Last edited by flyingatc; 10-14-2020 at 09:47 AM.

  10. #10
    Join Date
    Apr 2014
    Location
    Edmond, KS
    --
    2,531
    I put a 300EX carb on mine and I love it. If you look closely at the pic of the whole trike, you can just make out the yellow choke lever on the carb underneath the back of the tank.Click image for larger version. 

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  11. #11
    Join Date
    Sep 2011
    Location
    new york
    --
    50
    Hi.. did that 300ex carb bolt right on? Did you have this bog issue as well before the 300ex carb? Also, is there a particular year 300ex carb? Thanks.

  12. #12
    Join Date
    Sep 2011
    Location
    new york
    --
    50
    Update# 2: Today i set the clip in groove #3 (1/2 way). I also performed the slide/throttle sync, i noticed there was some play, so i closed it up some.. In groove 3 with synced slide/throttle valve, still bogging.. pilot screw adjusted in/out still Bogging.. One thing i noticed.. If i apply 1/2 choke and open the throttle quickly, it will not bog!! So it appears there is definitely an excessively lean mixture. Carb is off again, trying to locate or purchase an ultrasonic cleaner, with hopes of clearing some partially blocked passage!!

  13. #13
    Join Date
    Sep 2011
    Location
    new york
    --
    50
    Update-#3: Went with the 300EX carb. Carb was pretty dirty so i cleaned it all up. However the 300ex shindy kit did kot come with acceleration pump rebuild kit! So in The interim, i cleaned up the carb and went with the install to fit check it all.. fits like a charm must (def suggest removal of airbox for install) Big red no longer bogs.. however i feel it is really beggin for a shindy carb AND accel pump rebuild.. this will be performed when my kit(S) arrive! It rips pretty well, i am very pleased.. love the rapid acceleration.. I think it may be running slightly rich at idle, so on rebuild 2.0 i will tweak needle clip position.

  14. #14
    Join Date
    Apr 2014
    Location
    Edmond, KS
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    2,531
    The clip doesn't affect the idle mixture. There's a separate screw for this adjustment. I'm glad that you posted this. Mine has a very slight bog just above an idle that gets a little bit worse at higher altitudes. I may have to try some tweaking of the accelerator pump myself. It was worse before I adjusted the idle mixture screw. While messing with the carb swap, I also found out that the 250ES has a bigger main jet than the 300EX does, when everything's stock.

  15. #15
    Join Date
    Sep 2011
    Location
    new york
    --
    50
    Thanks!! So the only idle mixture control is the pilot screw?

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