2011 EC250 chamber moving away from flange?

[ec-txtr]

Hello, I have a 2011 EC250 Six Days that runs great with the exception that during rocky hillclimbs at high RPMS it will occassionally lose power and sound like the chamber has pulled away from the cylinder. It will correct itself and run fine again without me needing to stop but it always seems to happen again under similar circumstances and leaves me in the middle of a hill cussing.

I have tried new chamber mounts, new O-Rings, new springs (OEM), and repacked the Q-Stealth muffler. I also replaced the stock chamber with an FMF Gnarley after I crushed the stocker and it still does the same thing.

I was thinking of welding another hoop on the chamber to add a third spring or going with another muffler to reduce the backpressure.

Anyone experience this?

[(F5)]

You can run another spring or two, they don't last forever. Mounts can get a little sloppy too. Test in the carpark revving it and see if it moves. Hold your boot against the pipe.

But when was the last time you cleaned your powervalve? Can be done from the side with the pipe off. Also check the wire rod from the governor isn't hanging up on the side of the tunnel it passes through at base of barrel area. Sometimes they need a little tweak to stop this.

[blitz11]

I'd posit that it is the powervalve sticking open. You're cussing 'cause the valve is open, compression, and therefore power, is reduced.

[gasgasman]

+3 on the power valve being the culprit.

[ec-txtr]

Thanks for the feedback.
I just did the top end over the winter and the powervalve was clean and moving free, the rod has plenty of clearance to the case. The new top end didn't help, I have the same symptoms with the fresh piston and rings.

I've been reading more on this forum about the power valve free play and adding some preload so I will check that. Also may go with some heavier springs since the stockers are a bit weak looking compared to others.

I have revved it on the stand and see no signs of movement. It seems to happen on roots and rocks and it literally sounds like the chamber has popped off. Would a sticking power valve make it sound like the chamber has fallen off?

Appreciate the suggestions!

[Jacob 'Berg]

Originally Posted by ec-txtr

Thanks for the feedback.
I just did the top end over the winter and the powervalve was clean and moving free, the rod has plenty of clearance to the case. The new top end didn't help, I have the same symptoms with the fresh piston and rings.

I've been reading more on this forum about the power valve free play and adding some preload so I will check that. Also may go with some heavier springs since the stockers are a bit weak looking compared to others.

I have revved it on the stand and see no signs of movement. It seems to happen on roots and rocks and it literally sounds like the chamber has popped off. Would a sticking power valve make it sound like the chamber has fallen off?

Appreciate the suggestions!

Yes, the exhaust note changes dramatically. Had the same issue on my '05, power valve would stick open when hitting rocky terrain. You will also notice that the bike is making less power at lower RPM.

As others have stated, check the linkage. You may want to replace the PV bearings as well for good measure.