I am hearing a hissing from the front of my bike. It sounds like its coming from either the radiator or the engine block I honestly cannot tell.

I recently (600 miles ago) removed the airbox lid and replaced the filter with a uni filter, did a full oil change and oil filter change, put in a dynojet kit and put on a powercore 4 exhaust. Until today there has been no hissing at all, and when I went out for a ride today it started.

The noise does seem to get louder if I ride in the higher rpms AFTER letting off the gas, and quieter after letting off the gas while running at lower rpms. Another thing I noticed is that when not giving it gas while going down a hill the hissing is at its loudest.

I tried to do an audio recording, but the powercore 4 drowns out the sounds


I have been paranoid that there is something wrong with the radiator for a while, could that be it? If so what should I check? I also think every now and then the bike gets pretty hot, but it is also summer so I am not sure.

All help is appreciated

 

I doubt that it's from the rad. if you are not seeing and leaks. I would take a close look at the carb/intake and make sure that you don't have a vacuum leak. Use your ear to try and pinpoint where the sound is coming from.

 

Check around that carb for a vacuum leak. On a hill with closed throttle you vacuum is very high. This would make a vacuum leak louder. My first thought anyways.

See if you knocked the little hose off the top of intake.

 

What little hose are you talking about?

 

While you're at it check the joint between the slip-on and header. You may have a leak.

 

Probably the vacuum port to the pollution control valve. I'd think it would go ridiculously lean if that happened. But it could be a cracked hose.

Run the bike, getting down where you can listen for any sort of vacuum or pressure leaks.

 

Yes that hose ^ for the air injection control. I would also think it would be very lean unless you are jetted pig rich. Place to start anyways. Good luck!

 

Check rubber boot that attaches to back of cylinder.

 

Found the problem I think, hose that connects carb to cylinder. I did notice a faint smell of gas as well after being parked in the garage. Will give an update tomorrow when I can start it and not wake up all my neighbors. Damn you Powercore 4

 

Okay, so here is the video. The mic I used is pretty good, so with headphones you should be able to hear it. Is this an issue, or am I imagining this sound??

https://youtu.be/Z2vi_Nchz9Y