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Thread: KTM 300 EXC with a sky-high idle

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    Gimme six Schlitzes Beavis's Avatar
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    KTM 300 EXC with a sky-high idle

    I love two-strokes but this is starting to give me the shits. The KTM has been off the road for a little over a year. It has a Rekluse clutch which failed at Southwick last summer; the basket was torn to shreds and some clutch steels were warped to hell. So I parked it, bought a CRF250R for the interim and the KTM experienced some benign neglect.

    I got the clutch done late last autumn but the bodywork was a shitshow and the electrical system was worse. After doing the clutch, the idle was fine as I had to test the clutch engagement.

    I didn't ride it last fall and left it in the garage this summer. I finally gave it some TLC by replacing the wiring harness and replacing the kill switch. I also cleaned the air filter and replaced the spark plug. I tried starting the bike last week (first time since last year) and when I start it the idle is sky-high. It doesn't have a tach but it sounds like it's absolutely screaming.

    In all the time I've owned the bike, I've never touched the carbie. It starts first or 2nd kick, so I've never needed to touch it, meaning up until now I'd never looked at the jetting or anything.

    The bike has a VForce 3 reed system from Moto Tassinari, and the intake boot to the carb looked dry-rotted as fuck. Turns out the boot is ok, but I'll put in a new one anyway as soon as I get a new gasket from Moto Tassinari. In my haste, I pulled the carbie and stripped it. Threw it in the ultrasonic cleaner after that and now it looks fresh. Idle jet looks like a *40 and main jet looks like *165. The throttle action is clean and snaps open and closed nicely, so I don't think it's the throttle sticking or binding.

    New VForce gasket won't be here until Thursday, so I can't have it back together until then. In the event that replacing a boot (which didn't leak) and cleaning the carb (which wasn't dirty) doesn't fix the problem, what do I do with this cunt?
    Last edited by Beavis; 12-09-17 at 10:47 AM.

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    Non Compos Mentos Gammaboy's Avatar
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    High idle is probably an air leak. Make up some plates/bungs to block off the intake and exhaust port and do a leakdown test on it - it may have shat a crank seal while sitting and be pulling air through the bearing.
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

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    Gimme six Schlitzes Beavis's Avatar
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    Quote Originally Posted by Gammaboy View Post
    High idle is probably an air leak. Make up some plates/bungs to block off the intake and exhaust port and do a leakdown test on it - it may have shat a crank seal while sitting and be pulling air through the bearing.
    Is there an, uhh, easier way to do this? I really want to ride it this Sunday and don't know how much more time I can devote to fucking with it..

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    Non Compos Mentos Gammaboy's Avatar
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    if it's "screaming" it'll be a solidly fucked seal. Set air compressor regulator to ~5 or 10psi, duct tape over the reedblock and exhaust port, point air blower down plug hole, spray soapy water around the backside of the ignition rotor. Also check around the base gasket. Actually, if it's that fucked, I reckon it'd be hard to start.

    Throttle cable outer hasn't hung up on the barrel adjuster on the carb or throttle assy? Definitly getting a closed throttle?
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

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    Quote Originally Posted by Gammaboy View Post
    if it's "screaming" it'll be a solidly fucked seal. Set air compressor regulator to ~5 or 10psi, duct tape over the reedblock and exhaust port, point air blower down plug hole, spray soapy water around the backside of the ignition rotor. Also check around the base gasket. Actually, if it's that fucked, I reckon it'd be hard to start.

    Throttle cable outer hasn't hung up on the barrel adjuster on the carb or throttle assy? Definitly getting a closed throttle?
    The weird thing is the bike is still pretty easy to start. One or two kicks and off it goes. The throttle snaps open and closed fine, and if I put my finger on the carb itself I can "feel" the slide opening and closing.

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    Non Compos Mentos Gammaboy's Avatar
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    Can you see it pulling down to closed though?
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

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    Gimme six Schlitzes Beavis's Avatar
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    Quote Originally Posted by Gammaboy View Post
    Can you see it pulling down to closed though?
    I could see it closing, yeah, but I didn't verify if it was 100% totally and completely closed.

    If it's either the left side or right side crank seal, how hard are they to change? Do I have to split the cases and/or remove the crank? If yes, I'll fuck it off to a shop; if no, I could probably change them myself.

    I really hope it's just the carbie.

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    Non Compos Mentos Gammaboy's Avatar
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    When the throttle is closed, is there a coupl eof mm of play before anything starts moving?
    Crank seals are split cases, pull crank out.
    One side communicates with the clutch/gearbox, and if that one is fucked, it'll suck gearbox oil.
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

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    Gimme six Schlitzes Beavis's Avatar
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    Quote Originally Posted by Gammaboy View Post
    When the throttle is closed, is there a coupl eof mm of play before anything starts moving?
    Crank seals are split cases, pull crank out.
    One side communicates with the clutch/gearbox, and if that one is fucked, it'll suck gearbox oil.
    Yeah nah, I'm not splitting cases. Fuck me, if that's the case (har har) I will shit bricks. This thing has been ridden hard and put away wet (by the PO) and I'm sick of working on it...

    I'll double-check how much play with the throttle closed, tomorrow. Throttle assembly on the handlebar is from Domino, not sure if that's stock?

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    Quote Originally Posted by Gammaboy View Post

    Throttle cable outer hasn't hung up on the barrel adjuster on the carb or throttle assy? Definitly getting a closed throttle?
    Definitely worth checking this out at both the carb and throttle end. You can even tie wire the outer cable to the housing and adjuster as a safety precaution so they don't pull out.

    Jetting obviously depends on temp and elevation, but if it has been working okay up until recently there should be no reason to swap jets and needles.

  11. #11
    Gimme six Schlitzes Beavis's Avatar
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    Quote Originally Posted by fnlow View Post
    Definitely worth checking this out at both the carb and throttle end. You can even tie wire the outer cable to the housing and adjuster as a safety precaution so they don't pull out.

    Jetting obviously depends on temp and elevation, but if it has been working okay up until recently there should be no reason to swap jets and needles.
    Tying a wire is a good idea, thanks! I ended up ordering a new intake gasket, new carb bowl o-ring, new carb bowl drain plug o-ring, new carb mixture screw o-ring and a couple other very small bits and pieces. I don't expect any of this to fix it, as it wasn't leaking before, but I cleaned the carb as best I could. Got the gunk out with a toothbrush then threw everything into the ultrasonic cleaner with warm water and dish soap.

    Jet and needle were *40 and *165, the star meaning (I think) they're genuine Keihin. I've cleaned them and up they'll go back in.

    I'll see how it goes after the carb is back together. I'll check the throttle assy first. If the idle is still sky-high I'll add some more transmission oil, if it goes away then the problem is the right side crank seal. If the problem is still there after adding tranny oil.. I'm gonna set it on fire.
    Last edited by Beavis; 13-09-17 at 12:01 PM.

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    Quote Originally Posted by Beavis View Post
    Tying a wire is a good idea, thanks!
    Yep they are known for getting caught on the bar pad resulting in full throttle when you least expect it !

    Quote Originally Posted by Beavis View Post
    I ended up ordering a new intake gasket, new carb bowl o-ring, new carb bowl drain plug o-ring, new carb mixture screw o-ring and a couple other very small bits and pieces. I don't expect any of this to fix it, as it wasn't leaking before, but I cleaned the carb as best I could. Got the gunk out with a toothbrush then threw everything into the ultrasonic cleaner with warm water and dish soap.

    Jet and needle were *40 and *165, the star meaning (I think) they're genuine Keihin. I've cleaned them and up they'll go back in.

    I'll see how it goes after the carb is back together. I'll check the throttle assy first. If the idle is still sky-high I'll add some more transmission oil, if it goes away then the problem is the right side crank seal. If the problem is still there after adding tranny oil.. I'm gonna set it on fire.
    Yeah typically I run a 35 or 38 pilot depending on the needle i use and 165 main. This is on a 36mm carb at sea level say 20 degrees Celcius. I think pre 08 they had a 38mm carb.

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    Quote Originally Posted by fnlow View Post
    Yep they are known for getting caught on the bar pad resulting in full throttle when you least expect it !
    I don't have a bar pad; I have this weird steering dampener (not a Scott's or Ohlins or anyone recognizable) and it just doesn't work with the bar setup now. Oh well.

    Yeah typically I run a 35 or 38 pilot depending on the needle i use and 165 main. This is on a 36mm carb at sea level say 20 degrees Celcius. I think pre 08 they had a 38mm carb.
    I'll post pics, but the one thing on this bike that doesn't actually seemed fuck is the carb. That's why I'm ok with leaving the jets alone for now. Everything else has just been rooted. Brakes, clutch, electrical system, exhaust, cooling system, you name it...

    The carb has gone through the ultrasonic tank a couple more times since the pic so it's even cleaner. I ended up removing the air mixture screw and cleaning that up, as well as the choke. Overall, I was pleasantly surprised by how few parts are in the carb. Compared to the QuadraJet in the old El Camino, this Keihin is a cinch...
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