Noise coming from petrol cap?

[Dave M]

After bike idles for a few mins and then when I switch it off I can hear like a buzzing/slight hissing noise coming from the breather hole on the petrol cap?! Never heard this before? What is it?

[CaNsA]

[Dave M]

[ZRX61]

Some bikes are known for it, in the US a group of ZRX's sound like The Clangers TV show
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[yen_powell]

Dig a small trench close to where you park the bike.

If the fuel cap starts whistling quietly, jump into the trench.

It's just the hot engine making the fuel gases expand and they escape through the fuel cap key hole which is also a breather to stop your tank getting bigger when the gas expands and also allows the fuel system to suck fuel out of the bottom without it getting smaller or turning inside out.
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XT1200Z and a DR350 in bits

[Dave M]

[monkeybiker]

My Z1000 does it all the time, well not all the time but a lot. Apparently it's normal for this bike.

[Dave M]

[Rogerborg]

It would really help if you told us what bike. Kawasakis are famous for it, my GPZ whistled like a kettle.
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GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[Dave M]

It's a Yamaha yzf r125 with a fucked engine now apparently! See my other thread. This is the very least of my worries! One thing after another.

[RhynoCZ]

ZXRP1 also does that, nothing to worry about. When it does again, just quickly open the filler cap. It'll make a sound like when you open a beer.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[Tritey]

My GPZ 900 used to do that, sold it on and it probably still does!

[yen_powell]

I don't think I've ever had a bike that didn't do it.
____________________
Blackmail is a nasty word........but not as nasty as phlegm!
XT1200Z and a DR350 in bits

[kerr]

My zx6r does it, drove me daft trying to figure out where the noise was coming from.
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aprilia 125 Af1 Futura >> Suzuki gsxr 600 srad >> J1 zx6r >> cbr 600rr >> Speed Triple

[FirebladeRuss]

My '09 Z1000 sounds like the slowest whoopie cushion deflation ever on most days too.
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[ADSrox0r]

I had one that buzzed from the petrol cap at certain rev ranges, it turned out something was loose in the lock barrel and rattling around. Never could solve it, it was inside the barrel itself. Annoyed the shit out of me. Sold it. Cool story huh?
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Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[Ed Case]

Dunno about other brands but Kawasakis seem particularly prone to fuel tank 'whistling', my 6F does it.

[Snorty]

My ZX9 does it.
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Current: Yamaha FZ1 '07 | GSXR 750 SRAD

Past: CB125TDC | TZR125 | GPZ500 | CBR600F3 | ZX9-R | GSXR1000 K4

[Musketeer]

My ZX6Rs did that
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Current Bike: Yamaha XSR900 Previous bikes: Honda CBR1000RR Fireblade, Kawasaki ZX-6R Ninja, Aprilia RS125 2-stroke