Re occurring problem bike gets loud all the sudden

[perkybewbs]

I'm frustrated with this. I've had this happen before a while back and it happened again today. I have 2012 rmz250 that I have a somewhat new yoshimura exhaust on and later in the day at some point the thing just becomes super loud all the sudden. What could be the cause besides exhaust leaks or packing? Would boiling gas cause or the valves? Or is it because the engine has gotten really hot I just cannot figure this out. I have replaced the exhaust gasket at the cylinder head. I have completely taken the exhaust off and re fitted it. It does not do this at the beginning of my ride. Maybe I'm running too rich or something I just don't get it. Any help would be welcomed.

[ac717]

Has to be heat related. Check airboot connections and pipe connections. If I had to guess-probably in the silencer. Could be blown packing. If it was an exhaust air leak-would get popping I imagine. When you say loud we aren't talking knocks or tapping-just loud exhaust note??. Try the stock exhaust and compare.

[perkybewbs]

Exhaust note and loss of power. I only have 10 or 11 hours on the exhaust. If the packing is blown out would that cause the loss of power? I haven't ever had packing blow out in an instant like that before. In the past it just got progressively louder. Does the packing have anything to do with back pressure at all? The bike has a new oem piston installed 5 hours ago and valves were shimmed too.

Edited July 27, 2014 by perkybewbs

[pontiac252]

I think I'd look at the auto decomp mechanism, getting loud and losing power??

[perkybewbs]

I think I'd look at the auto decomp mechanism, getting loud and losing power??

Yeah it all of the sudden got loud and I feel a loss of bottom end power. I do have 11-12 hours on exhaust packing. Do 100% motocross riding so the bike is going pretty fast most of the time the bike starts easily. If it was the auto decompression mechanism would it cause the kickstarter to be soft? I would guess so. It did that a couple times. If the exhaust packing was blown out would that cause a noticeable loss of power characteristic? I assume that packing has something to do with back pressure as well.?

[Yamajeb]

If it was the auto decomp cam stuck open it would be very, very hard to start. If the cam were stuck closed it would start fine but power would suffer badly but all the time. If you end up needing to get back under the valve cover check proper operation of the cam but I don't think that's your prob.

Maybe reinstall the stock exhaust to help isolate the problem?

[perkybewbs]

If it was the auto decomp cam stuck open it would be very, very hard to start. If the cam were stuck closed it would start fine but power would suffer badly but all the time. If you end up needing to get back under the valve cover check proper operation of the cam but I don't think that's your prob.

Maybe reinstall the stock exhaust to help isolate the problem?

A stuck cam? I don't think the bike would run without a cam that sounds outlandish.

[Yamajeb]

"Cam" was probably a bad choice for a description. I'm not referring to the intake or exhaust cams, I'm referring to the auto-decomp "lever" that moves outward radially as the engine runs - sorry for the confusion

[perkybewbs]

Yeah I repacked the exhaust and it still does it. Any ideas about what this could be? Air fuel mixture?

[perkybewbs]

Both cams move freely I don't see any metal scoring or anything abnormal. I just checked the valves everything is in spec and I inspected camshafts and area around them INCLUDING decompression lever operation and free movement. Could it be a sticking valve or does the air screw need to be adjusted?

[springer28]

I'm pretty sure it's not your air fuel mixture you it would act up all the time in stead of just when it gets hot

[1fast250]

Get ya some carb cleaner or starter fluid while running spray lightly around the boot if idle goes up. Your issue is on the intake side and you have an opening. Keep an eye on the exhaust side that the copper gasket isn't shifting because of the heat.

[Shortrun]

Having the same type of problem but mine just got loud all off a sudden and its to loud hot/cold dossent mather.

Cant get my bike to pass the Db test. 
I repacked the exhaust twice just to be shure.
having the same loud problem with my Fmf 4.1 and the Db killer.

Any tips?