Kawasaki VN750 Forum banner

1 - 13 of 13 Posts

·
Premium Member
Joined
·
171 Posts
Discussion Starter #1
I took a really short ride tonight. I just wasn't feeling it, so I was back after 10 minutes or less. By the way, I picked up this 86 vn750 with under 8,000 miles on it, about a week ago. Everything on it has been just fine.

It has a trickle charging cable attached to the battery and sticking out of the seat, so I try to remember to keep that plugged in. I forgot to do it tonight, so I went out to the garage to plug it in, and I heard a little whirring sound.


Is this normal? Something to be concerned about?

I decided to start up the bike and maybe run it through a gear or two on the center stand, and then shut it down to see if it stopped. But about the time I backed it out of the garage, it stopped.

Oh, I should mention something: I replaced a turn signal two days ago. I bought the new one on ebay, and the seller claimed it was from an 86 (there's probably not much variation, if any, but I wanted it to match my bike as much as possible, and this one seemed to be in good shape). The repair was fairly uneventful, but it did require me to touch the electrical system a little. It was easy to figure out which cable was going to that turn signal, and there were little rubber splicers in there that made it downright trivial to plug in the new light. And it worked right away.

The only issue with the new turn signal is that I noticed that it turns off when I turn the handlebars all the way to the left (which is the side of the replaced turn signal). But I never turn the bars that far when I'm on the street, so I figured I would just take care of that "sometime," rather than this weekend. I think I'm going to replace the headlight soon anyway (with something brighter).

So anyway, being the troubleshooter than I am, I decided to turn the bars all the way to the right, to see if the sound changed when the light went out. Strangely, the light didn't go out. So this inconsistency with the light suggests that maybe something in the headline isn't quite as solid as I thought it was. And that might be the whole issue.

However, this is the first time I've heard this sound, so it could be unrelated to the light.
 
  • Like
Reactions: roadpouring

·
Registered
Joined
·
7,901 Posts
It's the vent in the gas cap. If you open the cap the noise will stop, but mine goes back to whistling pretty quick.
 

·
Premium Member
Joined
·
171 Posts
Discussion Starter #3
Well, there goes my electrical theory. Thank you very much.
 

·
Premium Member
Joined
·
377 Posts
Had the same whistle on my 750.
Remove the two screws next to the hinge under the gas cap.
Shot compressed air thru little black hole on top of tank under cap. This opening goes down a metal tube to the bottom left of tank next to rear tank attachment bolt. A black rubber hose fastens there and goes straight down thru a hole and hose ends towards the floor just in front of the center stand hinge. The hose will jump around when you blow air thru it depending on psi, so you may have to reposition.

You could blow air thru the little metal nipple that points downward into the forementioned little black hole without removing the cap hinge screws.
For thorough cleaning remove the cap and disassemble, but beware of the five springs spaced around the cap under the metal which pushes on the cap gasket. There are lots of other little parts that could be lost, as well.
 

·
Premium Member
Joined
·
171 Posts
Discussion Starter #5
OK, thanks. So based on that comment, it sounds like this hissing isn't what's supposed to be happening, even though it's not abnormal. It indicates that the vent needs to be cleaned?
 

·
Premium Member
Joined
·
377 Posts
Yes, vent and hose need cleaning.
Air should flow freely through vent without noise.
 

·
Registered
Joined
·
738 Posts
OK, thanks. So based on that comment, it sounds like this hissing isn't what's supposed to be happening, even though it's not abnormal. It indicates that the vent needs to be cleaned?
THIS IS NORMAL AND A GOOD THING! The whistling means that air is entering or leaving the gas tank. It means that your vent system is working properly. You need to worry when it does not whistle. You will normally hear it whistle after filling up with cold gasoline in a warm engine (gas expanding) or as the bike sits and cools off (gas contracting).
 

·
Registered
Joined
·
738 Posts
Yes, vent and hose need cleaning.
Air should flow freely through vent without noise.
Not true, unless you remove the fuel separator in the gas cap. The whistle in this case is causes by air passing through the narrow section of the separator (see below). It is also the source of some POOG problems.
 

·
Premium Member
Joined
·
377 Posts
Not true, unless you remove the fuel separator in the gas cap. The whistle in this case is causes by air passing through the narrow section of the separator (see below). It is also the source of some POOG problems.
A whistle certainly indicates air travel, which is good and hopefully avoids the POOG episode.

I'm certainly no expert on these things, but from recent experience with two 750s, a 2005 and a 2006, I now hear 'whooa' air travel and no whistle.

The 2005 had a POOG episode and a frequent whistle. We blew out the little black hole and the metal nipple on the cap and now there is no whistle and no POOG episodes, but there is air flow through the vent line.


The 2006 had be sitting for five years and would have a noticeable whistle when parked after riding. I assume that pressure builds in the tank from heat and the swooshing of fuel and is then released thru the tank vent.
Because this bike had sat for so long and there was gunk all over the cap and tank from fumes, I disassembled the cap and cleaned it thoroughly but did not permanently remove any internal parts. Since then, there has been no whistle but there is a definite air transfer.

I reckon some will whistle and some won't but with the whistle, at least it's certain that air is moving.


One other thing.... when we first blew both tank vents, we heard a sound from both vent hoses that sounded like a pea-shooter as though there was a projectile particle exiting the hose.


Again, I'm no expert but just citing my recent experience and whatever the particular problem, it won't hurt to do a thorough cleaning, that is, unless you break something, strip a screw hole or lose parts in the process.
 

·
Registered
Joined
·
1,277 Posts
I love the "what the fk is buzzing?" video!

The gas got warmed up by the engine, and is expanding faster than it is being consumed by the engine. Totally normal. It stops as the bike cools off.

It's basically a mini-whoopee cushion. The fact that it makes a sound indicates that it is able to build up pressure and release it at a very specific pressure, meaning the rubber in the vent is pliable and seals well. Don't go blowing pressurized air & possibly debris through there unless you get into a POOGS situation due to a blocked line or channel.
 

·
Premium Member
Joined
·
171 Posts
Discussion Starter #12
I love the "what the fk is buzzing?" video
Honestly, I'm just stoked to see a YouTube video of my hand turning the key on and off on a 750. I've been looking forward to owning one for a long time, and I'm very happy with it. And very happy with this forum, of course.

I'm glad I did the video, though. It was quick and easy and a lot easier than explaining what I was hearing.
 
1 - 13 of 13 Posts
Top