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

  • Hi everyone,

    As you all know, Coffee (Dean) passed away a couple of years ago. I am Dean's ex-wife's husband and happen to have spent my career in tech. Over the years, I occasionally helped Dean with various tech issues.

    When he passed, I worked with his kids to gather the necessary credentials to keep this site running. Since then (and for however long they worked with Coffee), Woodschick and Dirtdame have been maintaining the site and covering the costs. Without their hard work and financial support, CafeHusky would have been lost.

    Over the past couple of weeks, I’ve been working to migrate the site to a free cloud compute instance so that Woodschick and Dirtdame no longer have to fund it. At the same time, I’ve updated the site to a current version of XenForo (the discussion software it runs on). The previous version was outdated and no longer supported.

    Unfortunately, the new software version doesn’t support importing the old site’s styles, so for now, you’ll see the XenForo default style. This may change over time.

    Coffee didn’t document the work he did on the site, so I’ve been digging through the old setup to understand how everything was running. There may still be things I’ve missed. One known issue is that email functionality is not yet working on the new site, but I hope to resolve this over time.

    Thanks for your patience and support!

250-500cc Wr300 Surge At Idle And Decel

X

xeridad

Husqvarna
A Class
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.
 
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.
 
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.
 
xeridad said:
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.
Click to expand...
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.
 
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