Been lurking here for a while...first time poster.

I bought a '97 Fat Boy last year that just hit 30,000 mies, so I started doing some of the 10,000 service work on it a week ago. Changed tranny and primary oils so far. Also took the pipes (V&H longshots) off and rattle canned them black since I had to get to the tranny anyway.

After reassembling and riding, there's a hissing sound that seems to be coming from the air cleaner. Goes up and down right with the throttle/RPM's. Pretty sure it's air being sucked in, but I don't remember hearing that before.

It's got a Stage 1 SE. Inspected the K&N filter when everything was off but didn't see any dirt so I didn't clean or mess with it; just reattached it.

Wondering what this can be. I don't wanna ride if I'm risking damaging my engine.

Any ideas/insight is welcome. Thanks.

 

Here's a video that captures the sound happening:

 

Get some carb cleaner and spray around the seals and the back of the carb and see if rpm's go up.

 

Did you possibly disturb your crank vent system ? Loose top breather bolt maybe. And what Texas said, welcome from Connecticut BTW.

 

Put a bolt in that center hole you're sucking air through it. See how it sounds then.

 

Thanks for the replies guys. I'm gonna try all of those suggestions.

I had the air cleaner cover on and was riding when I originally heard the sound. It's way more obvious with it off. But yeah, I didn't think to put the bolt back in and see what the difference is.

 

Just to update, I put the bolt back in and it sounded the same. Tried spraying around with carb cleaner and no RPM difference.

On a whim, I thought maybe I had an exhaust leak as I was getting some popping on decel, so I took off the pipes again and replaced the gaskets (didn't think to do that when I had them off before--although the old ones looked fine). Same sound still.

Brought it by my indie. He didn't think it was an unusual sound (said his Dyna makes the same noise), although he thought the bike might be running lean and thought I should clean out the carb and see how it does.

I've never done that, but from reading up I feel like I could handle it. In the meantime, he thought there was no problem or danger riding it as is. Still bugs me because I'm sure that sound wasn't there before I pulled/painted the pipes and changed fluids.

 

check where the filter mounts to the backing plate, make sure it's tight there too. I'll try to make a video for you this weekend of mine, there's definitely intake noise, I don't think it sounds much different than yours, but I couldn't hear the sound you described either, just the intake sucking in lots of air.

 

Mine definitely makes a "sucking" noise at certain throttle settings. It's a function of the "open" air cleaner and a close fitting cover in my case.


Also check to make sure any vacuum hoses are properly connected and not cracked (petcock and VOES, if equipped). If not, make sure any unused vacuum ports in the manifold or carb are properly sealed.