1. 2 Stroke Husqvarna Motorcycles Made In Italy - About 1989 to 2014
    WR = 2st Enduro & CR = 2st Cross

250-500cc Wr300 Surge At Idle And Decel

Discussion in '2 Stroke' started by xeridad, Sep 7, 2019.

  1. xeridad Husqvarna
    A Class

    Location:
    Albuquerque
    Husqvarna Motorcycle:
    2009 WR300
    Other Motorcycles:
    '76 Honda GL1000
    I've moving this over from Thumper Talk now that I'm registered here. :)

    This is quite the issue, and has me and my mechanic guessing.
    The primary issue is a surge at idle once the bike has warmed up. The bike starts, runs, and accelerates, but when I let off the throttle, rolling or still, it goes "gungk, gungk, gungk" at short and slightly irregular intervals. The other issue is that the idle screw on the carb must be turned almost all the way in to get it to idle.

    We carefully and thoroughly rebuilt and jetted both the Kehien PWK 38 and the stock Mikuni carbs. We reasoned it was likely rich jetting; it wouldn't tolerate the choke, the plug was wet after idle, and we could turn out the air idle screw all the way to make it run better. It still ran really rich at idle despite the smallest available idle jets, and the surge remained no matter what. I'm convinced it's not a carb problem.
    We've also replaced the reeds and the reed block gasket, and have sprayed cleaner around the engine to see if we could detect air leaks while it was running--nope.

    So what's left?

    The previous owner did the top end just before I bought it, but used black RTV sealant instead of a base gasket. It looks like a messy seal and the heads sits so low on the engine that the cylinder touches the clutch cable. I've read about high compression, squish, and port timing issues, so next on my list is to put the standard base gasket on to see what that does.
    I've gotten comments that the surge seems like a lean condition (despite the rich symptoms at idle), so maybe there's a problem with the crank seals. There is no gear oil consumption, however. After the base gasket, I try crank seals.

    Anyone else have this issue? Any insights or suggestions are appreciated.
  2. xeridad Husqvarna
    A Class

    Location:
    Albuquerque
    Husqvarna Motorcycle:
    2009 WR300
    Other Motorcycles:
    '76 Honda GL1000
    Update: Replaced the base gasket. No dice--same issue.

    BDLH1018.JPG IMG_1574.JPG IMG_1575.JPG
  3. xeridad Husqvarna
    A Class

    Location:
    Albuquerque
    Husqvarna Motorcycle:
    2009 WR300
    Other Motorcycles:
    '76 Honda GL1000
  4. Dirtdame Administrator

    Location:
    Rock Springs Wy
    Husqvarna Motorcycle:
    11 WR300,13 WR125,18 FE501
    Other Motorcycles:
    17 Beta Xtrainer
    The surge is definitely NOT caused by a rich condition. Surging is happens when there is a lean condition. These bikes will leak at the reed valve intake gasket when the reed boot gets old or damaged....at least on the 2010-11 models. If you have an oily sparkplug, it could be caused by a rich condition somewhere other than off idle, or from a worn crank seal on the clutch side. Air can also get in through a worn crank seal on the ignition side, but that would likely make the bike run lean throughout the range. Check your reed intake boot and gasket first. Use some gasket sealant there as well.

    The pilot circuit will need a pilot jet that allows you to get the maximum best tuning at between 3/4 to 1 1/4 turn out on the air screw. If you have to go all the way in, you need a bigger pilot jet, and if you have to go down, you need a smaller pilot jet.
    shrubitup likes this.
  5. PawPaw Husqvarna
    AA Class

    Husqvarna Motorcycle:
    2013 TC 449
    Other Motorcycles:
    Honda Crf450R + old CB750
    A small air leak will also cause this issue.

    Paw Paw
  6. shrubitup Husqvarna
    AA Class

    Location:
    Seattle WA
    Husqvarna Motorcycle:
    '00 TE610 (pretty much a WXE610)
    Other Motorcycles:
    Husaberg FE450, KTM 200EXC, Triumph
    2001 Honda CR250 reed valve gasket fits. I had a 2014 WR300 and replaced my OEM gasket with the Honda gasket five years ago anyway.
    Borntoride71 likes this.
  7. xeridad Husqvarna
    A Class

    Location:
    Albuquerque
    Husqvarna Motorcycle:
    2009 WR300
    Other Motorcycles:
    '76 Honda GL1000
    Thanks for the replies. I did follow that thread earlier, and both the reed block gasket and the reeds themselves have been replaced. I’m waiting on the stator puller tool and will do the crank seal on that side next.

    As far as jetting goes, I think it’s ok at 410 main and 30 pilot—it runs great under throttle. When I increased the pilot jet size to 32.5 and 35, the surge remained, but with rich characteristics: a deeper sound and blubbery, boggy throttle response.
  8. Dirtdame Administrator

    Location:
    Rock Springs Wy
    Husqvarna Motorcycle:
    11 WR300,13 WR125,18 FE501
    Other Motorcycles:
    17 Beta Xtrainer
    I'm running the stock Mikuni with a #35 pilot, #80 starter jet, #4 slide, JDjetting "rich" needle and a 440 main jet. I ride the bike mostly between 3000 and 5000 ft. altitude. It's nice and punchy from bottom to top.