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Off idle hesitation is killing me

Discussion in 'XJ Technical Chat' started by pillowmaster50, Oct 1, 2013.

  1. pillowmaster50

    pillowmaster50 Member

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    So this problem didn't exist when I acquired the bike in 2007. It has slowly been getting worse and worse... My nice paved road is closed now so I have to ride on unpaved, pot-holed, wash-boarded, switchbacky, dust cloudy, sheer-drop-offy, generally terrible mountain back-of-the-woods roads--where I spend most of my time right between idle and like 1/8 throttle... which is where my bike doesn't like to run.

    So here are some symptoms:
    -Not as bad when cold, worse when hot.

    -If the bike has been idling for awhile, like at a stoplight, then I have zero power when I go to take off. I have to rev the engine before there's any chance of forward movement (I swear I'm not a douche). So when the lights about to change, I twist the grip to about 1/2 of WOT and I get a sputter sputter blub blub vroooommmm! and then even if the rpms drop back down to idle speed, I'll have power when I go to take off.

    -I got some 38 pilot jets (stock is 40) (I live at high altitude) and I thought it would improve things, but it didn't. When colortuning, I screwed the mixture screws all the way in, then backed out until the cylinder starts to fire again, then further until the cylinder is firing almost every power stroke, then I have to stop because if I go out any further then I'll probably loose the screw on the road. So I can't even get yellow at idle with these pilot jets. Now, with the colortune in, I rev the engine and the combustion goes YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW (while sputtering and hesitating) until about 3k rpm where it turns blue again (and goes vrooooom).

    -Once I'm out of the dead zone, the bike runs like a bat out of hell.

    -This symptom has progressively been getting worse over the years. It has survived several carb overhauls and keeps getting worse. The symptom first started to happen before a valve adjustment about 5000 miles ago (I know fitz, I'm due) and was not affected by the adjustment (unless I'm not remembering correctly)


    Other maintenance that didn't help:
    -I just did another carb overhaul. I even invested in a cheap harbor freight ultrasonic cleaner this time. Float heights are perfect. Passes clunk test. Carbs are as shiny as 30 year old aluminum can be.

    -New air filter

    -New spark plugs

    -Sync and tune. Well not really tuned to where I'd like them but still. And I only burned myself once this time.

    -New airbox-to-carb boots (carb-to-engine boots seem ok to me. #4 has some bigish cracks but they don't go all the way through).

    -Adjusted (manual style) cam chain tensioner.

    -Prayed to Jesus.





    Please help me I'm going crazy!
     
  2. Polock

    Polock Well-Known Member

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    put your 40 pilot jets back in
     
  3. RickCoMatic

    RickCoMatic Well-Known Member

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    You NEED to run Stock Pilot Jets or one size larger.

    Failure to "Get-out-of-the-hole" without hesitation is a function of the Pilot Jet supplied Fuel to IDLE the Bike ... PLUS supply additional "Supplemental Richness" to sustain combustion(s) at the instant the Bike transitions from IDLE to OFF IDLE.

    Try the hotter Jet.
    Colortune to get BLUE.
    Add richness until the BLUE fades away.
     
  4. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    Did the carb overhaul include a full teardown for throttle shaft seals?

    Have you replaced the vacuum port caps?

    If you know it's time to check the valve clearances again, do it. You can't solve a carb issue with out of spec valves. Then do a compression test to see what's up with the motor.
     
  5. pillowmaster50

    pillowmaster50 Member

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    Thanks for the suggestions guys. The problem is that the bike runs rich right off idle. Going back to a 40 pilot would make it worse. (Remember I'm at high altitude... I've been tuning bikes to run up here my whole life. If this was a regular carb I would have taken it smaller than a 38) I will try going back to the 40 though this weekend just for shits and giggles. The throttle shafts were replaced last summer and the problem persisted through. There's something gradually getting more and more out of whack as the years go by I think.
     
  6. webofdeception

    webofdeception Member

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    it sounds like its literally just slowly dying... keeping an eye on this thread though. an interesting issue for sure, considering all that you have done thus far. good luck!
     
  7. KrS14

    KrS14 Active Member

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    I would run your float levels lower, say 15mm instead of the normal 17mm spec. I'm thinking you're getting too much gas coming from your mains when you open the throttles at all.

    I have a similar issue :)
     
  8. Polock

    Polock Well-Known Member

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    " There's something gradually getting more and more out of whack as the years go by I think."
    i just had a birthday and i completely agree. :)
     
  9. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    How about maybe?

     
  10. Rice_Burnarr

    Rice_Burnarr Member

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    If you're running rich at idle and adjusting the idle mixture screw doesn't take care of it, then I'd look at the enrichment linkage and seals next. Maybe you're choke is hanging up, or maybe your choke plunger seals aren't making a good seal against their seats?
     

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