Hey there, i have a 250 Megelli motard and there is a strange hissing sound eminating from what seems to be inside the engine. I cant even say how long its been there except that i only noticed it ever since a friend of mine pointed it out to me.
Initially i thought exhaust gasket, but thats been replaced and still no change in the hissing sound. Then i took the carb out and put it back all nice n tight but no difference still.
Is there anything else to check or could this just be the way the engine sounds? Hmm.. Could a hole in the piston cause a hissing sound? i have red lined the bike in all gears and no smoke at all from the exhaust.
Im at a loss. next week i will do a compression test and listen to the other bikes like mine to get a better understanding. Also gonna ask the mechanics whats going on but i dont have much hope because the last time i complained about the sound, they said its normal.

 

It's not a hole in the piston.

 

I also want to add that the sound is there wether the engine is hot or cold. Its there all the time and is in sync with the engine. If the rpm goes up then so does the hissing sound speed up. The weird thing is that if i lean the bike over side to side, the sound sometimes becomes quieter for a few seconds. Almost like the oil inside is moving over the 'leak'. Quite confusing.
What about a bent valve?

 

If you had bent valves or any internal motor probs I'm pretty sure you'd know about it!

If you have all your smog stuff on still I'd check there, sounds like a vacuum leak to me.

Check all the rubber air hoses. Check the air box for a hole.. There's not too much that it could be, should be easy to locate.

good luck

 

+1 on the vacuum leak, if it's constant hissing than a cap/plug may have fallen off, or has dry rotted. Check all your vacuum connections whether you have the smog crap on or removed.

 

NOT a hole in the piston, NOT a valve. Don't go looking for trouble.

"If its not broke, keep fixing it till it is"

David

 

what is smog stuff? My air box / intake pipe is far away from where the sound is. Could it be from the crank case breather system? Hmm, maybe i should check that out too.

 

The smog junk is the black looking tube that sits on the spark plug side of your engine just atop the head cover. That line is under vacuum and injects air into the exhaust to attempt to "clean up" the exhaust a bit more, KAWI calls it the KCR air suction system or something to that nature. If it's removed there are a few mods you need to do, such as the blocking plate, the carb vacuum line, and the airbox line. These all need to be plugged if the smog crap is removed. I would not suspect the crankcase vent as the orifice is very small and i doubt you would be able to hear a hiss coming from that line.

I'd snoop the vacuum connections and see if you can detect any leakby there. If not then as David says, If its not broke, keep fixing it till it is

Check out dirtsurfer's post, he has alot of good pictures of the smog junk. Once you know what it looks like, you will know whether you have it or not.

https://www.kawasakiforums.com/forum...ead.php?t=8886

Good luck,

Anthony

 

Ok well i dont think my bike has smog stuff on it. I did mention in my first post that its not a kawasaki but a megelli. I am from indonesia, not USA.
Well ok if they say keep fixing it untill its broken then i cant say anything more. Just that i find the sound very annoying, especially at high rpm. I am actually in process to sell the bike but everyone who comes to look at it, is turning me down because of the sound.

 

Can you make a wave file?

So we can hear it?

David