I have a 2012 Street Glide with Screaming Eagle intake, PowerCommander, and Rinehart true dual full exhaust.

I was heading down the interstate to NC about 100 miles into the ride I stopped for gas. When I attempted to restart the bike, it turned over but kinda backfired through the intake with a puff of white smoke. I looked everything over but couldn't see anything obviously wrong. I did find a small, hard rubber cap (see pic) laying on the crankcase so I picked it up and put it in my pocket.



I hit the start button again and it turned over and started right up. The only thing was now I could hear a loud vacuum "hiss" but couldn't locate hoses loose or missing. I went ahead and rode to my destination-the bike runs fine with no problems-just the constant vacuum "hiss".

Once I had a chance to look closer I found a metal tube on top of the motor (see pic) that looked like the rubber cap could have come off of it. I had a chance to look at some bikes at the dealership and noticed that the same tube had the rubber cap on. While running, I can cover the tube with my finger and that is definitely the source of the vacuum "hiss". I installed the rubber cap back on the tube and went for a ride but when I would slow to a stop and pull the clutch lever the bike would shut off. This happened several times. Also, it barely idles with that plug on. Pulled the cap off and the bike runs good as ever.



Any idea why this is happening or should I even worry about it?

 

put the cap back on, that's where it goes.
If the cap has gotten too hard or is cracked you can get a new one at any auto parts store.

also your bike needs to relearn it's idle. Install the plug and ride it for a while.

 

Thanks much!

 

Old thread but I just noticed mine is missing and there is a hissing noise. I think it's been this way for a while. Runs great now but wonder if it will run better when I put one back on? Just have excessive blow by which is why I started messing around in this area.

Did your bike get back to normal when you put it back on and ran it for a while?

 

Yes put it back on. There's a reason that the vacuum port is capped off.

 

Yes, mine is running just fine now. I put the cap back on and went riding for a couple of hours. Idled rough for a little while but it re-adjusted itself for the correct fuel/air mixture and she is running great now-just got back from Daytona last week.


Good luck!