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Thread: Cold acceleration

  1. #1
    CAL0987
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    Cold acceleration

    I have a 1998 F650 that i noticed lately as it has gotten colder out that the acceleration is very sluggish.
    It gets better as the engine warms up.
    Definitely much better when the choke is on, which is needed to even get it to drive.

    But I noticed today that even after riding for 30 minutes and letting the engine warm , that when i turn down the choke, that the acceleration is still lackluster.
    When I turn the choke back up it accelerates like i feel it should.

    And i don't think i should drive with the choke on all the time!
    Carburetor adjustment needed?
    Something else?
    Just serviced the carbs , but did not make any special adjustments, except idle to factory spec.

  2. #2
    Quote Originally Posted by cal0987 View Post
    I have a 1998 F650 that i noticed lately as it has gotten colder out that the acceleration is very sluggish.
    It gets better as the engine warms up.
    Definitely much better when the choke is on, which is needed to even get it to drive.

    But I noticed today that even after riding for 30 minutes and letting the engine warm , that when i turn down the choke, that the acceleration is still lackluster.
    When I turn the choke back up it accelerates like i feel it should.

    And i don't think i should drive with the choke on all the time!
    Carburetor adjustment needed?
    Something else?
    Just serviced the carbs , but did not make any special adjustments, except idle to factory spec.
    There is an often cited rule: go back where you were last. It sounds like with the choke off it is running lean but using the choke enrichens it so it runs better. So I would check for partially clogged jets or some other reason it is running lean.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  3. #3
    CAL0987
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    Replaced the jets when i did the carbs.. at least i think i did... i assume they come with the carb kit.
    I also put in an inline fuel filter after the tank valve?
    Is there something i can adjust to change the Lean?

  4. #4
    Quote Originally Posted by cal0987 View Post
    Replaced the jets when i did the carbs.. at least i think i did... i assume they come with the carb kit.
    I also put in an inline fuel filter after the tank valve?
    Is there something i can adjust to change the Lean?
    Idle mixture is adjustable. Fuel level in the float bowls should be checked. If it is too low the bike wil run lean. Fuel float level is adjustable.

    I would verify that the needle jet and is correct for that bike. I am not sure if the needle position is adjustable on those carbs but if so raising the needles one notch might fix it.
    Last edited by PGlaves; 01-01-2021 at 02:10 PM.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  5. #5
    SURVIVOR akbeemer's Avatar
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    This exchange is a demonstration of the corollary to the quote in Paulís signature line (The greatest challenge to any thinker is stating the problem in a way that will allow a solution.) The corollary is that hardest part of fixing a mechanical problem is determining what needs to be fixed. I find that I have a fair ability to fix mechanical problems, but unfortunately a mediocre ability to determine what problem requires fixing. Thankfully this forum provides valuable assistance in diagnosing problems.
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  6. #6
    Quote Originally Posted by akbeemer View Post
    I find that I have a fair ability to fix mechanical problems, but unfortunately a mediocre ability to determine what problem requires fixing. Thankfully this forum provides valuable assistance in diagnosing problems.
    On several occasions I have opined that electrical problems are usually the easiest problems to fix. And on an equal number of occasions I have been challenged and derided for that opinion. Until I explain that they are almost always easy to fix but range from difficult to impossible to find. Happy New Year.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  7. #7
    CAL0987
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    Quote Originally Posted by PGlaves View Post
    Idle mixture is adjustable. Fuel level in the float bowls should be checked. If it is too low the bike wil run lean. Fuel float level is adjustable.

    I would verify that the needle jet and is correct for that bike. I am not sure if the needle position is adjustable on those carbs but if so raising the needles one notch might fix it.
    Yes, when I serviced the carbs, i did adjust the float level by bending the levers on te floats...

    I just regret having to take the carbs apart again!!

  8. #8
    CAL0987
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    Finally getting around to working on the bike again!
    Mostly from the fear of having to get out the carbs again!
    Just got my thumb screwdriver in, so adjusted the idle mix screw form 3 turns to 4... seemed to change the acceleration form blah with the choke off and good with the choke on, to good with the the choke off and great with the choke on.
    With the choke off I get hesitancy accelerating, and with the choke on, i get no hesitancy, great acceleration.
    Next step is to try 4 1/2 Turns of the idle mix screw?

  9. #9
    CAL0987
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    Rode it some more with the screws at 4 turns...seemed to be better when I got the cobwebs out and properly warmed up. But seemed to still get better acceleration when the choke was on.

  10. #10
    Registered User
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    I took the inline filter off my '97 as its not needed IMO. I finally did that after a buddy from the Harley world told me some gravity systems are very sensitive to flow. My bike performed better when I removed the filter. There are two screens before the carb, one in the tank and then one inline before the carb. Never had an issue.

    Also there were issues with some older carbs getting tears in the vacuum membrane at the top of the carbs which will definitely affect performance. You can inspect and replace those with using a right angle phillips head without removing the tank but its tight.
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  11. #11
    CAL0987
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    Looks like there is a possibility that some bad gas might not have been helping... after a recent fill up it seems to be preforming better...

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