gas tank vacuum

racer · May 22, 2006

Yesterday, after letting my fuel level drop to one bar, I removed the gas tank so I could insulate the bottom of the tank and remove the the rubber pieces between the tank and frame to let the heat escape. Also did the Cromit mod and unhooked the center throttle return spring.

Buttoned it all back up and went for a test ride. After three or four miles, I pulled over to fill the tank. When I opened the gas filler cap, I heard a whoosh that sounded like the tank was under a vacuum. Is this normal or do I have a vent tube pinched off?

I rode for about an hour after that with no problems.

Anybody know anything about this?

SQUIDO · May 22, 2006

racer said:
Yesterday, after letting my fuel level drop to one bar, I removed the gas tank so I could insulate the bottom of the tank and remove the the rubber pieces between the tank and frame to let the heat escape. Also did the Cromit mod and unhooked the center throttle return spring.
Buttoned it all back up and went for a test ride. After three or four miles, I pulled over to fill the tank. When I opened the gas filler cap, I heard a whoosh that sounded like the tank was under a vacuum. Is this normal or do I have a vent tube pinched off?

I rode for about an hour after that with no problems.

Anybody know anything about this?

normal

FJRocket · May 22, 2006

No, that's not normal, Abby. That sucking sound you heard was induced by the gas pump and it's effects on your wallet.

Yep, had it happen on mine, too. Still seems to work ok. 25K and still sucking gas, air and money.

Rogue · May 22, 2006

Mine has never done that, at least one member had his tank collapse from that.

radman · May 22, 2006

The tanks not venting. The pump is powerful enough so that if on a trip, and emptying a full tank, it will collapse and destroy the tank. Either a vent hose is pinched, or blocked with debris. Flush the hose using brake clean down the little orange doughnut at the rear of the cap well. Check to see that during the tank install you didn't pinch one of the vent hoses.

racer · May 22, 2006

I didn't see a tank vent hose on the bottom of the tank when I removed the tank, just to hoses on the left side and two on the right side. Where does the tank vent to, the gas cap?

radman · May 22, 2006

The two small diameter hoses on the left side are vents-one vents the tank. the other drains spillage from the cap well. When you spray brake clean down the hole at the back of the well, you will see it drain from the hose at the bottom of the bike-if it's flowing. If not, find out why. This is a maintenance item that should be done every oil change, as that hose likes to plug with road debris.

racer · May 22, 2006

Thanks Rad, I'll check it out tonight.

Woodstock · May 22, 2006

radman said:
...the other drains spillage from the cap well.

Damn. And all this time, I've been wondering why everyone was putting on fuel cells, when I thought I've been able to put 11-12 gallons in the tank. :huh:

Afast03nNJ · May 22, 2006

That wasn't vacuum, it was pressure. Gas tanks are supposed to hold a slight amount of pressure so they don't let vapors out into the enviroment. Cars do the same thing when you open the gas tank cap. The EVAP system in cars will hold most of the vapors and burn them off through the motor. Bikes don't have that system, so vapors will vent off when the pressures get high enough.

Do check the vapor hoses to make sure they aren't pinched, but I don't think you have anything to worry about.

Bike Effects · May 22, 2006

radman said:
The tanks not venting. The pump is powerful enough so that if on a trip, and emptying a full tank, it will collapse and destroy the tank. Either a vent hose is pinched, or blocked with debris. Flush the hose using brake clean down the little orange doughnut at the rear of the cap well. Check to see that during the tank install you didn't pinch one of the vent hoses.

Absolutely correct. The tank is not venting and it will be damaged. Vent hose!

Bustanut joker · May 22, 2006

Absofokinlootly on the vent!

Noobs ! <_< When they gonna learn?

:jester:

odot · May 22, 2006

Hey, bust....who cares? They are here for our enjoyment. Of course, rad is too......

Bounce · May 22, 2006

1. Check the bottom of the vent hoses. Clean them. Then cut them at a 45° angle facing toward the back of the bike. This will reduce how quickly spooge gets drawn up into the hoses as you ride.

2. PM of the filler neck: https://www.bikes-n-spikes.org/maint/ff/ff.html

racer · May 23, 2006

Well okay, now we're getting some where. Thanks Bounce. Just goes to show ya, not everyone here knows what they're talking about. We've gone from "normal" to "clean the vent or the fuel pump will collaspe the tank" to "it isn't vacuum its pressure build up".

Seriously, I appreciate all the help.

Groo · May 23, 2006

We're not all experts, but some of us did stay at a Holiday Inn Express last night....

Hope you get it sorted out.

radman · May 23, 2006

To be honest, the "pressure build up" wasn't germain. No offense, but the poster wasn't aware of the history on this problem

Though, on a Cali bike, it might have merit, as they use a closed vent system.

Bustanut joker · May 23, 2006

Groo said:
We're not all experts, but some of us did stay at a Holiday Inn Express last night....
Hope you get it sorted out.

Well,, I just saved a ton of money on my car insurance

!

I'm not allowed in the Holiday Inn, Wifey don't like the company I keep there

:jester:

dgfella · May 25, 2006

I'm still waiting to hear if the dealers are repairing crushed tanks under warranty. Mine is collapsed on the bottom. I haven ot yet taken it to the dealer for repair/replacement, because I don't want the bike down during riding months.

If anyone has approached their dealer about this, please let me know how it went.

dgfella

gas tank vacuum

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