EC300 Peculiar Noise (Again)

[xdab]

Have been reading with interest F5's 4/12/12 post regarding EC300 lost power and rattle. Has made my head swim. I have what may or may not be similar problem, as follows.

At indiscriminate times my 2011 EC300 will go soft on power which is accompanied by a sound like the silencer has fallen off. Sounds real loud and raspy for a second or two. Power is noticably off for an instant but I can blip the throttle and everything returns to normal. Can not associate this occurance with engine being under load, or anything else for that matter. Happens a handful of times during course of a race. Again, the sound happens for a two count like pipe has come loose or something but quick return to normal.

I've done all the obvious stuff. Pipe and silencer mounts are tight, installed new exhaust o rings and springs, plug looks good, carb removed and cleaned, PV assembly cleaned, inspected and working like it should. This situation differs from F5's in that it's not characterized by a rattle as much as it is a brief sound like an open expansion chamber on a 1974 CZ. Something ain't right.

Theories?

[jostby]

I had that happen to me only once. I quickly shut off the bike, got off and looked it over. Scratched my head a time or two then restarted it and the noise was gone. It's never done it since and I've always wondered what caused it. It was almost like someone pulled the pipe off the manifold. Curious to see the response you get.

[Jakobi]

I'm still going to go with powervalve. The one time my powervalve stuck wide open the bike genuinely felt so underpowered and like a bucket of bolts. The exhaust note was so far off that I thought I'd blown a bottom end.

[forgiven]

Last ride of the year...last year I had thebsame thing. Haven't really had a chance this year but was hoping it was water. Very unnerving. I have a 2010 300. My power valve had to be adjusted when new since that was fairly common. It ran fine till then.

[forgiven]

It would be sure nice to figure this out. If it were the powervalve it would be the second power valve issue. Is there certain things to do to prevent the power valve from sticking?

[Jakobi]

When you look at the pv assembly and particularly where the drums run the cylinder it reallyu is easy to see how even a small bit of carbon could cause teh valve to stick for a moment. How long since it was last cleaned? It should be easily able tot do the 100hrs between top ends. Also might depend on the brand of oil you use and how close the jetting is.

[husley]

I have had the exact same symptoms, 2010 300 75 hrs.

I guess I will be inspecting my PV. Also anyone know what size orings are used on the exhaust/pipe flange? Or should I just purchase OEM?

[forgiven]

I prolly got 75ish hours as well. Short of dismantling...how do you think I could clean it in place?

[Jakobi]

You don't have to pull the head or cylinder to clean the pv. The hardest part is getting the flapper out. You kind of have to turn the engine until the piston is at bdc, push the flapper in, turn it sideways and then pull it out.

http://www.gasgasons.com/index.php?s...c&staticID=133

The O-rings are 44mm id x 3mm wide. Use Viton rubber as it'll last a bit longer. I usually use a good smear of RTV Red high temp silicone to ensure a super seal.

[(F5)]

Do read up about float height as well, as they can be a betch to set & mates have had them all over the place.

My std now is get it till it floods on the sidestand & then back a bit. i used a vernier to measure the amount the tang is bent so you can adjust it back a little.

Nice to hear how it goes.