Fuel cap

A whole section dedicated to the Suzuki Burgman
Post Reply
User avatar
2wheelover51
Posts: 1102
Joined: Fri Aug 07, 2015 9:12 pm
Current Ride: 2012 Burgman 400 Limited
Location: Poole, Dorset

Fuel cap

Post by 2wheelover51 »

Last night when I parked up I got some strange "groanings" from the fuel cap area, and again this morning when I took the cap off to fill up there was a big whoosh of inrushing air into the tank. I assume the cap is the vent to the tank, but examining and cleaning it today it doesn't seem blocked, but sucking on the inside or trying to blow from the outside doesn't allow a great deal of air to flow in. I've looked in my Haynes manual but the fuel cap doesn't seem to get a mention. Is there a known problem (and solution) here or is it just Burgman 400 "character"? It hardly seems enough air flow is going in to offset the petrol use and I'm sure it wasn't doing it when I bought the scoot.
Any advice greatly appreciated.

Whatsisname
Benefactor
Posts: 886
Joined: Thu Apr 16, 2009 5:06 pm
Current Ride: Burgman 400 K5
Location: Sunny Bournemouth

Re: Fuel cap

Post by Whatsisname »

The whoosh hasn't been unusual on my Burg, but the only groaning I've noticed is from me as I get on!
I wake up every morning with a smile upon my face,
My natural exuberance spills out all over the place!

User avatar
Data
Benefactor
Posts: 2557
Joined: Wed Feb 08, 2012 6:43 am
Current Ride: Vespa GTS300ie abs asr
Location: Now getting closer to the Essex Sunshine Coast, South Eastern UK

Re: Fuel cap

Post by Data »

It's normal 2wheels. They all do it and it's a big characteristic of fuel injected bikes. Some have vented tank caps but many don't. That sort of thing can be controlled by the fuel pump these days especially when it's mounted inside the tank. My Vespa GTS groans and 'farts' after a run too. All normal.

User avatar
smeghead
Benefactor
Posts: 2081
Joined: Wed Oct 24, 2012 2:58 am
Current Ride: GTS 300 Touring
Location: Doncaster

Re: Fuel cap

Post by smeghead »

Data wrote: Fri Jun 18, 2021 4:38 am It's normal 2wheels. They all do it and it's a big characteristic of fuel injected bikes. Some have vented tank caps but many don't. That sort of thing can be controlled by the fuel pump these days especially when it's mounted inside the tank. My Vespa GTS groans and 'farts' after a run too. All normal.
Mine too, sounds like whale song and can last ages.

User avatar
2wheelover51
Posts: 1102
Joined: Fri Aug 07, 2015 9:12 pm
Current Ride: 2012 Burgman 400 Limited
Location: Poole, Dorset

Re: Fuel cap

Post by 2wheelover51 »

Thanks guys.
That's stopped me getting my drill out and adding a few more vents! I can only think that it's become more "vocal" as the weather's warmed up. ;)

Rocketman122
Posts: 237
Joined: Fri May 29, 2020 2:15 pm
Current Ride: eee

Re: Fuel cap

Post by Rocketman122 »

so let me tell you. my b400 did the pshhhhh sound on oepning the cap on HOT days. I had this recently with my maxsym 600. in fact even more than that.

at the start of some hot days, on in particular I came to open my cap as normal, it grumbled and hissed and a HUGE eruption of fuel shot out. not a little squirt and not a quick half a second shot. a huge eruption that shot out to around chest height. by instinct (it took me a second or two to think if it would subside or should I close the cap) I closed the cap quickly. a puddle on the floor and all over the plastics and seat. something is off and till Iget a chance to figure it out, im just riding with the cap sitting on top of it but not locked. some vaccum issue

on another day I was on the highway (also a hot day) and it ran very badly. it slowly over the distance ran like it was getting less and less gas. I got into a gas station, limping there. I oepned the cap, very very slwoily. filled it up as I thought It might have been contaminated gas with a lot of water in it (as I have seen in a video) and it ran fine. on the way home, it did the same, and since that day, around a month ago, and having experienced that geyzer, I run with the cap unlocked. I am considering drilling a hole in the cap, but more so I think im having crud in the tank and the pathetic filter at the bottom of the fuel pump assembly IN the tank is clogged and as well will add an inline fule filter and clean the tank to get it nice and clean. will remove the injector out and clean that as well as im also having performance issues with what Is its showing it running lean.

watch this video



he had what I had. I never thought it could exist so I always open the cap without thinking twice. then it shot out like crazy and for a long time. it wasnt a small squirt. it was a scary geyzer shoting out.

User avatar
2wheelover51
Posts: 1102
Joined: Fri Aug 07, 2015 9:12 pm
Current Ride: 2012 Burgman 400 Limited
Location: Poole, Dorset

Re: Fuel cap

Post by 2wheelover51 »

Wow! I can only think that as the breather is inadequate, it's allowing the tank to be distorted by the vacuum inside, as the fuel is used. This same vacuum will lower the boiling point of the fuel which will then start to boil, and as the pressure is released back into the tank is pushing the frothing fuel out through the open cap. It's just a theory, but explains why it only happens in the warmer weather.. It sounds like it could all be overcome by providing a bigger breather hole, or as you say riding with the cap lose..:roll:
Will have to experiment...

Post Reply