Keihin FCR troubles
  • RedneckRider181
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    Keihin FCR troubles

    by RedneckRider181 » Mon Jan 31, 2011 12:41 pm

    Havent been on here in awhile, but i know where to come to get correct advice.

    Im having trouble with an FCR carb. Been through it a couple times, had to rejet and adjust to get it idling and running right, but still having some trouble.

    After being on the throttle, it wont idle back down after letting out of it. It will run at about 2500 rpm for about 5 to 10 seconds before going back to idle speed. Cables arent binding or anything. Wondering what the problem could be.

    Thanks.
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    paul turner
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    by paul turner » Mon Jan 31, 2011 1:00 pm

    Lean on the bottom of the circuits. Try a new pilot jet, verify the fuel screw is put together correct. Spring, washer, o-ring, in that order.


    Paul
    If you ain't crashin', you ain't ridin' :-)
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    AgentSmith
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    by AgentSmith » Mon Jan 31, 2011 2:01 pm

    Also, make sure that the passageway above the pilot jet is open and flowing freely.

    This must be done after the carb is disassembled and the slide is removed.

    Using a small gauge wire, pass it through the hole above the pilot jet until it comes out cleanly into the venturi. After it's clean, shoot carb cleaner through it until a strong stream sprays up into the venturi.
    "Make a man a fire and he'll be warm for a day.
    Light a man on fire and he'll be warm for the rest of his life."
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  • RedneckRider181
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    by RedneckRider181 » Mon Jan 31, 2011 2:38 pm

    At first it wouldnt idle at all. We backed the mixture screw out as much as possible and it didnt phase it. So i went from a #40 to a #45 to get it to idle at all. Mixture screw is around 1 1/2 turns. All jets are clean. Had it apart two or three times.
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    Krannie
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    by Krannie » Mon Jan 31, 2011 4:23 pm

    Have you looked at the slide plate?

    The front of the slide has a plate in it that is held in by friction, with an o-ring. It can come loose and cause hanging idle. I've seen it on (5) FCR carbs now.

    Glue the plate back in place with 3M weatherstrip adhesive. Use sparingly.
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  • RedneckRider181
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    by RedneckRider181 » Tue Feb 08, 2011 6:05 pm

    Just wanted to say thanks for all of your help so far.

    I had the carb back off and apart, pilot mixture screw was correct, and i also went ahead and used the weatherstrip adhesive on the slide plate. Haven't got the bike completely together yet, so idk how it will run now.

    Another detail i left out that might be helpful... Sometimes the exhaust header on this bike glows red hot. It has clean radiators and a good coolant flow, so that's not the problem.

    I seem to think it is getting air somewhere it shouldn't be. That could explain the odd high idle, the hot running, and the white color of the spark plug. Moved the needle clip from the 3rd to the 4th position to try and compensate for the lean condition, but it's not gonna fix the air problem if there is one...

    Any ideas?
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    dlpmx
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    by dlpmx » Wed Feb 09, 2011 1:06 pm

    It is definitely lean.The way I find air leaks is spray a little carb cleaner or ether where you think the leak is.If the engine changes you've found the leak.Be very careful not to spray the exhaust or around anything hot and have a hose near by just in case.If I was a betting man I'd put my money on the pilot circuit being clogged.I think this because when you changed the air screw nothing changed.Take out the pilot jet and spray carb cleaner through the jet till clean then spray into the jet hole on the carb until it is open.

    Dale
    All mods listed in the Garage
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  • Sir O.T.B.
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    by Sir O.T.B. » Wed Feb 09, 2011 6:13 pm

    paul turner wrote: verify the fuel screw is put together correct. Spring, washer, o-ring, in that order.


    Paul

    Does the washer go on the T handle end of the spring or the pointy end?
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    Krannie
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    by Krannie » Wed Feb 09, 2011 6:49 pm

    Sir O.T.B. wrote:
    paul turner wrote: verify the fuel screw is put together correct. Spring, washer, o-ring, in that order.


    Paul

    Does the washer go on the T handle end of the spring or the pointy end?


    o-ring / washer / spring/ screw
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  • Sir O.T.B.
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    by Sir O.T.B. » Fri Feb 11, 2011 11:09 pm

    Krannie wrote:
    Sir O.T.B. wrote:
    paul turner wrote: verify the fuel screw is put together correct. Spring, washer, o-ring, in that order.


    Paul

    Does the washer go on the T handle end of the spring or the pointy end?


    o-ring / washer / spring/ screw


    The o-ring that I have is to big to fit in the hole in the carb. :( :?:
  • dobent4@yahoo.com
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    by dobent4@yahoo.com » Sat Feb 12, 2011 5:33 am

    The spring goes on first, as in the first thing you slide on the fuel screw.
    Then the washer goes on.
    Then the o-ring goes on.
    What was the last thing anyone touched on the carb before this problem arose ? Don't rule out anything. You mentioned 'had to re-jet'. Well, with the exception of drastic temp and elevation changes and without major intake/exhaust changes there's no need to re-jet a bike that had been running fine.
    Usually something like a partially plugged pilot happens and the owner feels its a jetting problem. It is, but not the one he thought. :lol:
    Look very carefully at your manual, note how that plate goes on the carb slide. A cursory glance will have most people installing it wrong, and the symtoms can be similar to yours. Look at it carefully.
    Be sure you have that fuel screw set-up right too.
    All ti headers on modern thumpers will glow and can be seen clearly in the right lighting . However, the white plug is serious business, this problem needs fixed ASAP.
    There's no reason in the world to run the motor longer than a minute, 2 minutes tops, while you check your work. Doing so could cause some real problems.
    This problem is related to something that happened when you decided to re-jet and took it apart.
    Let us know what you find. Doug
  • dobent4@yahoo.com
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    by dobent4@yahoo.com » Sat Feb 12, 2011 5:46 am

    The o-ring that I have is to big to fit in the hole in the carb.

    Immediately begin chewing on it.
    Get the right one. :lol: Doug

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