My new 2010 KTM 400 XC-W was running like crap

[Mike_in_Ontario_Canada]

After 5 hours of riding the bike during breakin, it started to have odd symptoms, it would have a racing idle, or it would stumble and die. Sometimes quick throttle bursts help, but the problem kept returning when it was hot.

I started looking at the vent lines, if there was something clogging them, and came across a vent line that was completely pinched between the crankcase black vent tube and the carb.

Here's where the pinched pink carb vent line is located:




I cut the section of the pinched vent line off, and routed it a bit rearward so it would not get pinched.


Here's the section of the vent line that I cut off, it was even discolored due to heat from the engine vent line, assuming as the bike warmed up over time, heat encouraged pinching / deforming the line.


Just a heads up to check your vent lines, seems to be a factory assembly thing to be aware of if your new bike starts having similar issues. Bike runs so much better now, just like new. Great bike too.

Regards,
Mike

[Duke]

Nice detective work and a great tip.

[Mike_in_Ontario_Canada]

Thanks, it was a great ride today, 3 hours or so of single track stuff, bike idled nice even when it got hot. I think the pinched hose caused some sort of vapor lock problem. Instinct of venting seems to go back to the days tinkering with my old muscle cars with carburetors..

Cheers,
Mike